Methuselah Syndrome

The tendency for ancient and fantasy settings to show humans having very long lifespans despite the lack of any established medical science. People will routinely live to a century or better while remaining lucid and active. Might or might not be explained as A Wizard Did It in the case of magical characters. Because in fiction age automatically equals wisdom rather than, say, the gradual death of brain cells, he frequently is an Old Master or a mentor. (Of course, research on senility-due-to-age has been skewed by mental illnesses like Alzheimers; people without those diseases can do very well, but those diseases are all too common.)

Interestingly, this seems almost a complete inversion on the myth of people in the past rarely living till old age, which is mostly the error of averaging the historically high child mortality rate.

Not to be confused with Improbable Age. If there's only one or a few characters like this, especially cute little girls in a Bishoujo Series, it's Really Seven Hundred Years Old.

Anime and Manga

 * Ranma One Half gives us both Happosai and Cologne, two ridiculously skilled martial artists nowhere near slowing down (despite both being very old and crinkly) at the age of at least 120 (manga) or 300 (anime).
 * There's also Rakkyousai, Happosai's cohort in the manga, and Chingensai and a whole bevy of Miniature Senior Citizens in a late Filler episode of the anime.
 * In One Piece, Word of God has stated any human can live to be 140 and apparently some (or at least Kureha) are so badass they can easily live much longer.
 * The humans do seem to get old at the same time as real humans, though. Whitebeard was 72 and had many problems with his health due to old age. Rayleigh seems to be about same age as Whitebeard, and Garp, being 19-year-old Luffy's grandfather, is probably in his 60's or 70's - both of them have complained of not being able to perform their usual feats and tire easily because they have gotten old.

Film

 * A lot of movies and shows with Buddhist monks tend to do this. Kill Bill, for example, establishes Pai Mei as being either well over 120 or more than a thousand years old, depending on whether you want to go by the original script (which states that Pai Mei was already a martial arts master in 1883), Real Life (where he was in 1647 if not earlier), or the actual film (where David Carradine ad-libbed the line into "one double-aught three", or 1003). No explanation is given; it's implied that Pai Mei is just that Badass.
 * Deeply ironic when one considers that the entire point of Buddhism is not to live forever - a person becomes a Buddhist monk to end the circle of rebirth into this Crapsack World of ours.
 * Buddhism has a concept known as Bodhisattva, which means a person who consciously rejects Nirvana to help others to achieve it, and may spend dozens of reincarnations in this work. But Pai Mei is not a Buddhist monk by a long shot. His philosophy appears to be Taoism in extremely dark bent. Buddhism is only one of three traditional religions of China, along with Taoism and Confucianism.
 * A condition possessed by J.F. Sebastian in Blade Runner, which is ironically an inversion seeing as Sebastian's Methuselah Syndrome means he dies quicker as opposed to living longer.
 * Godzilla is stated to be a dinosaur that was somehow still living underwater, who was then mutated and provoked by the bombing of Hiroshima and Nagasaki. Either there is an entire colony of Godzillasaurs living in secret, or he's been alive for at least 65 million years. The former possibility has some logic to it, since the original film killed him at the end, and all later films star a different individual.
 * Ahem From a Single Cell, or judging by the size, some wads of skin.
 * The protagonist of Film/Earth2100, Lucy, has lived to be 91 years old and still in pretty good shape, while most of the world's population has died off from diseases and starvation.
 * Mr. Jingles in The Green Mile, a mouse that lived some 70 years.

Mythology and Folklore

 * A staple of Mesopotamian Mythology. The first two dozen or so kings in the Sumerian King list have reigns that last anywhere between 100 and 43,200 years - the record being held by King En-men-lu-ana of Bad-tibira. Nobody seems to have had a normal-lasting reign until after Gilgamesh.

Literature

 * The Trope Namer is Methuselah from the biblical Book of Genesis. He lives 969 years, longer than any human in the Bible. That said, most humans from before the flood have a given age of several centuries. It is only after the flood that God decrees that humans will live a "mere" 120 years or less. There are several figures after this point who are said to have lived just over one hundred, which is technically possible but still unlikely for an ancient Hebrew. In the books after the Pentateuch, which took place much closer to the time of the lives of their writers, people live somewhat more reasonable lifespans.
 * Merlin, in most versions of the King Arthur mythos.
 * In The Lord of the Rings, the Númenóreans, or Men of the West, had extremely long life-spans granted to them when they were given Númenor. Aragorn lived to 210, and the fact that most men of Númenórean descent had much shorter lives was mentioned as a sign of the sorry state the world was in.
 * Part of the explanation for the men of Númenór... well, no, just the royal line (including Aragorn) being so long-lived is because their first leader, Elros Tar-Minyatur, was a half-elf who chose to follow his human side. Despite choosing mortality (unlike his brother, Elrond), he still had a greatly extended lifespan: he reigned for 410 years until his death at 500 years.
 * Harry Potter has many of these. Magical ability seems to automatically prolong one's lifespan. Some characters experiencing this are:
 * Dumbledore, who was somewhere upwards of one hundred, possibly one hundred and fifty (several different ages have been given). In the sixth book he says that he does not expect to live to the end of the year, but this is only because of a cursed ring he foolishly tried to wear.
 * Bathilda Bagshot, who was the aunt of Dumbledore's contemporary and almost outlived them both.
 * Professor Marchbanks, proctor for the O.W.L. exams seen briefly in the fifth book, mentioned that she personally tested Dumbledore when he was a student.
 * Ron's Auntie Muriel, who in spite of everyone else made it over a hundred.
 * Hagrid is only in his sixties at the time of the books, but does not have a single gray hair on him.
 * Hagrid is also half-giant, so it's not just about being a wizard, in his case.
 * Channelers in the Wheel of Time series live much longer than non-channelers. Aes Sedai are routinely at least two hundred years old, and it's discovered in the series that their upper limit of around 300 is a side effect of the Oaths they swear; those who haven't sworn the Oaths can reach beyond that, to four hundred or more. (Male channelers presumably would have the same conditions, except for the whole "Power drives them insane" factor.)
 * A side-effect of practicing sorcery in the Belgariad is indefinitely-increased lifespan. Except for the characters who become sorcerers during course of the main story, every magic-user in the books is at least one thousand years old.
 * Roland, in The Dark Tower, although that's mostly because the collapse of his world has made the nature of time's passage murky at best.
 * In the world of The Dresden Files, it's established that wizards just plain live longer than normals, with 200-300 years being average. A doctor, having seen a series of Harry Dresden's X-rays (when he can get the machine to work, anyway) theorizes that his cells are much better at repairing themselves than those of a normal person.
 * In Sewer Gas and Electric, Kite is a one-armed Sweet Polly Oliver Civil War veteran, and is over 170 years old. No special reason; she's just a tough ol' broad who never got around to dying.
 * The original Redwall book actually had a very old character named Methuselah, who was killed about midway into the book. Also, it's noted that badgers, especially Badger Lords, can live four times longer than the other species - most of Mossflower's creatures measure time in "seasons", so evidently Mossflower's badgers age at the same rate as real-life humans.
 * Humans in the Bible Times era of Many Waters age incredibly slowly, reaching adulthood around 100.
 * Wizards in Discworld who are competent enough to live to 60 without being assassinated will most likely make it well past 100. The oldest wizard mentioned in the books, Windle Poons, makes it to 130.
 * This is made even more impressive since the disc runs on Alternative Calendar where a year is equal to 800 days. This means that in regular earth years Windle nearly reached the age of 285.
 * The Star Wars Expanded Universe book The Courtship of Princess Leia had a 100% human character who was over 300 years old. While it's not explicitly stated what planet's years that referred to, later sources indicate that her homeworld has 491-day years, meaning that in Earth years (or the very similar in-universe Coruscant standard years) she's closer to 400 years old. Either way, she's implied to have used The Force to extend her lifespan.
 * In Moses Man of the Mountain, in agreement with the biblical account, Moses is somewhere upwards of ninety by the time of his death, and he even says that if he wanted to he could have easily gone another ten or twenty years. Similarly, his supposed brother Aaron makes it over a hundred.

Live-Action TV

 * Cinderella in The Tenth Kingdom is a highly amusing parody of this trope. As one of the Five Women Who Changed History (and the only one still living), she is over 200 years old, yet looks only middle-aged and still quite beautiful due to 'magic surgery.' However, this does not extend beyond the surface--not only does she hack, cough, and nearly pass out from the various ailments she suffers from, but during her dance with the Dog Prince, her bones audibly creak and she ends up stuck bent over backward, needing help upright again.

Tabletop Games

 * In Dungeons and Dragons, high-level monks, druids, and some other classes have an ability called "timeless body". While it doesn't lengthen their lifespans, it does render them immune to aging penalties (bonuses still accrue) all the way up to the moment of a death by natural causes.
 * Other methods to be human and either age gracefully or live a long time: the epic (for characters of level 21+ only) feat Extended Lifespan, which can be taken multiple times; and taking levels in the Ruathar prestige class, which is the game's mechanical way of saying "elves have blessed you and call you friend".
 * In Magic: The Gathering, people of the plane of Ravnica have significantly longer life spans; the main character is well over a century old, and still an active law enforcement agent.
 * This may be because Ravnican years are shorter than Earth years; after all, the Guildpact has been around for ten thousand years.
 * Also, while he's over a century old, he does think every so often that a hundred is too old for law enforcement work, has a few problems with his age, and it doesn't help that he's been overusing magical health packs for a while.

Video Games

 * The Telvanni grandmasters in The Elder Scrolls: Morrowind are extraordinarily old even for a species with an average lifespan around the neighborhood of 500 years.
 * Wang from Tekken is (as of Tekken 5, at least) 104 years old. He seems to have some back problems (one of his opening poses), which mysteriously vanish whenever he's beating ass in the tournament.
 * In the Zork chronology, both Dalboz of Gurth and Mir Yannick lived for a very long time. That's justified because Dalboz cast a spell on both of them. Played straight, however, are the examples of one of the King Zylon (the Aged) and Antharia Jack, who both lived for a very long time for no apparent reason.

Western Animation

 * A few characters in Avatar: The Last Airbender are in their 100s, and this isn't viewed as anything especially unusual by the cast. The co-creators Hand Waved it by loosely comparing it to the concept of Xians, Taoist immortals who could live up to half a millennium. However, they admit that they did it primarily for plot-time purposes and didn't learn of the mythology until long afterward. Kyoshi supposedly lived to be over 200 and looked largely the same the entire time.
 * Fire Lord Sozin died in his sleep at the age of 102. Then again, he is the ruler of the Fire Nation and could afford a long lifespan, plus it's mentioned that he may have used the power of the comet named after him to extend his lifespan. Bumi is 112 and still physically active. Supposedly, Guru Pathik is 150, though this is never actually mentioned in the show.
 * Kyoshi was 230, the longest-lived avatar; she may have looked the same in all appearances, but she did wear pretty heavy makeup. If we assume there is no interregnum or regency in the Fire Nation, Sozin must have died only 29 years before the series starts (in a flashback to 6 years ago at Azulon's funeral, it is stated he reigned for 23 years, 23+6=29), which would make him 152! and the longest-lived non-avatar mentioned. See all the nerdy details here.
 * The creator Ret Conned Azulon's rule from 23 years to 75 years.

Real Life

 * Henry Clay and John C. Calhoun. Seriously, these guys never died. Clay and Calhoun were elected to Congress as Jeffersonian Republicans (AKA Democrats) in 1810. Henry Clay then went onto a long political career, ran for president of the United States three times (1824, as a Democratic-Republican, 1832, as a National Republican, and 1844, as a Whig) before dying as the Civil War approached. Basically, he lived through four party changes, and when he died the Whig party pretty much fell apart. Calhoun didn't live as long, but was John Quincy Adams'  Vice-President, and then went onto a very long political career that involved practically getting the South to secede from the United States in 1850. They may not have lived to be 600 years old, but Clay and Calhoun are mention more often in the AP US History book than George Washington, Lincoln, FDR, and pretty much any president. Clay, in fact, is mentioned in one book starting about page 200 and then dies on page five-hundred six.
 * John Adams, the Founding Father and 2nd President of the U.s.A. lived to be 91. In the early 1800's, 91!
 * Not that Clay and Calhoun aren't examples of awesome and all.
 * William Jennings Bryan!
 * A British example would be Lord Palmerston, who entered Parliament in 1807 and only left it on his death in 1865, two days short of his 81st birthday.
 * Or Gladstone, who was over eighty when he became prime minister for the last time, and was generally referred to as the Grand Old Man. (He's sometimes referred to just as "the GOM" in the same way that the Republican Party is the GOP.)
 * Éamon de Valera joined the Irish Volunteers in 1913, fought in the 1916 Rising and was elected to the Irish parliament in 1918. He retired from politics in 1973 when his second term as President ended.
 * Jeanne Louise Calment lived to be 122. She was born in 1875 and died when the Spice Girls were topping the charts. She was married for 48 years but still spent 55 years as a widow.
 * The reason the average life expectancy in olden days was lower than it is now was because of the significantly higher infant mortality rate, which brought down the average. If a person managed to survive past early childhood they actually had a good chance of living into their sixties, seventies, or even eighties. Sometimes they would even live longer than that; Pope Agatho was born in 577 A.D. and died in 681 A.D., making him 104 years old when he died. Then again, being Pope would give him all the best food, lodging and medical attention known to mankind.
 * Though this may also be a clerical error. At the time years weren't being kept track of quite as meticulously as later centuries. This is also why we don't actually know the real date of Jesus's birth, as it was counted backwards at this time period by people with incomplete archives.
 * According to Tradition, John the Apostle lived to be 109. Again, the Tradition component is with regard to his birth year; he is known to have died in 115 AD. During his life, there were rumors that he would never die, but instead live to see the return of Jesus, and he was the only Apostle to die of natural causes.
 * Some monarchs are known to also be this, such as Queen Victoria for the UK and Emperor Franz Josef of Austria-Hungary. Coincidentally, his descendant Otto von Habsburg, had he ruled, would have given both of them a run for their money: born before World War One, he died in 2011; if he had actually taken the throne in 1922 (when his father historically died, but after the abolition of the monarchy in Austria) and lived as long as he did (i.e. to 2011), he would have had an 89-year reign--the longest ever.
 * Jack Nicholson and Michael Caine are the only two actors who have been nominated for Oscars in The Sixties, The Seventies, The Eighties, The Nineties, and the Turn of the Millennium. We're still waiting to see if this will extend to The New Tens.
 * Dick Clark has often been cited in various media as immortal, including in a song written for/about him by Benny Mardones.