Old soldiers never die; they just fade away.
The Old Soldier is the grizzled veteran who has been through and seen everything in war. He would more than qualify for being a Shell Shocked Senior, both in age and experience, but he's still going into battle and odds are that he's the backbone of whatever unit he or (more rarely) she is in. This character type is almost never an officer or a commander, and is instead usually a Sergeant Rock. Generally you can expect them to be tough, to have a few badass scars, and to be eternally pissed off at (or at least exasperated by) the younger troops around him. Despite that, he may still turn out to be one of the best sources of mentoring or seasoning a young soldier can get.
Expect the Officer and a Gentleman to rely on him quite a bit in running the unit, ala Captain Smooth and Sergeant Rough. Ensign Newbie, on the other hand, will rarely know to do this or will actively tick off the Old Soldier in attempting to control a unit, a mistake he usually pays for. Despite the first page quote, old soldiers have about a 50-50 chance of dying in a work of fiction, but usually not until rather late in the story, generally in a Heroic Sacrifice of some kind or in a suitably impressive way. If this character dies early in a story, odds are you're dealing with a story on the cynical end of the scale, and that it's going to have a high Mortality rate.
If the soldier is too old to fight, but denies that fact, he may be a Perilous Old Fool.
- In one of the Star Wars Expanded Universe "Empire" comic lines, The Rebellion finds Able, an old clone trooper who has been living in the wilderness since the Clone Wars. He eventually gets incorporated in Luke's unit and proves to be the best, if most cynical, soldier there and looks out for Luke until the whole unit gets wiped out by The Virus.
- Whatever Happened to the Caped Crusader? has Batman coming face to face with a vision of his mother (whether it's a Dying Dream, regular dream, Fear Gas trip, genuine psychic vision etc. is never revealed) that basically pegs him as this. She says that none of the various Batman versions in the multiverse ever give up. They keep fighting until they drop, whether it's saving the world or a single person, whether on his first time out or his thousandth. Also, she states that he never goes to Heaven or Hell, instead his afterlife reward is to be Batman. The same soul is continually reincarnated into every universe to keep up the fight, making Batman older than every single superhero in DC and Marvel combined seeing as at one point there were infinite universes. Whether or not this is true is up for debate, though the ending seems to show him being reborn as a baby.
- Wallace from Sin City has utilizes this trope, although he's a bit more laid back than most versions. Most people don't realize that he is a retired Navy Seal until he has to prove it to them.
- Wolverine is sometimes written this way. You could especially see it in the late 80s, when he was Storm's second-in-command in the X-Men.
- We Were Soldiers: Sergeant Major Basil Plumley. Both the real one and the character played by Sam Elliott.
- Heartbreak Ridge: Gunnery Sergeant Highway. Being played by Clint Eastwood helps.
- Stripes: Warren Oates as Sergeant Hulka.
- The Thin Red Line: Nick Nolte as Lieutenant Colonel Tall. They don't come much more grizzled.
- Les Dillon, a Marine sergeant from a Harry Turtledove pair of novels where in World War II Japan invaded Hawaii rather than simply bombing it.
- Broxigar "The Red Axe" of Warcraft definitely qualifies. As an orc who lived through the wars of all three games, he was greatly respected by Thrall and revered by the soldiers. Despite his age and maturity, he gets a good amount of Character Development through his Survivor Guilt.
- Sergeant Jackrum from Monstrous Regiment. It's not clear how long he's been a soldier, even to him, but his most recent term of service was supposed to be twelve years, and he managed to keep ahead of the discharge papers for another four years after that.
- And though not technically soldiers, the Silver Horde consists of consists of barbarian adventurers who are all at least eighty. The fact that they are all still alive after more than half a century each in a line of work that kills most people that go into it in a year or two means that they are very, very good at not getting killed.
- Kat from All Quiet on the Western Front.
- Starship Troopers: Sergeant Zim (no relation), and a few other veterans like Jelal probably qualify.
- Ser Rodrik Cassel from A Song of Ice and Fire. A tough, loyal, dependable and sensible knight, who, unfortunately, is very much given the short end of the stick in the series.
- In the Harry Potter books, Aurors are somewhere between cops, spies, and soldiers, but Alastor "Mad-Eye" Moody and Rufus Scrimgeour unquestionably fit this trope. Mad-Eye specifically is covered with war wounds, he's an old friend and confidant of Dumbledore's and considered by Dumbledore to be the most trustworthy and reliable wizard in England. Sure enough, when the Order of the Phoenix gets back together (with many roster changes) Moody is part of its backbone. His death early in the last book is a big sign of just how harrowing things are going to be.
- The Warlord Chronicles: Most of the characters who survive until the third book are Old Soldiers. Sagramor, who has been a soldier nearly his entire life and main character Derfel are major examples, but one of the coolest examples is Culhwch. There's a bit very close to the end of the series where he walks out in the space between two opposing armies and dares someone from the other side to try to become famous by killing him in single combat. When no one comes out, Culhwch taunts the entire army about their cowardice and reluctance to take on a bald old man. When Culhwch turns his back to return to his own side, one of the enemy Mooks does in fact try to backstab him, but Culhwch effortlessly guts the poor bastard. He then waits for a minute to see if anyone else is going to come forward before really returning to his place in the shield wall.
- Sergeant Jean in Seven Men of Gascony by R. F. Delderfield. Nicholette is this in a sense and is an interesting enough character to deserve mention. She is a camp-follower selling refreshments to Napolean's army, not a soldier per se (that is she doesn't carry a musket). However she grew up in her circumstances and was an Old Lady of War at age sixteen. She knew the tricks of surviving including those specific to her circumstances such as avoiding giving away more of those kind of refreshments than she was willing to give by the adroit use of a Death Glare, and by a non-canonical(presided over by the sergeant not a priest that is) but faithfully kept marriage to each of the members of The Squad until they were killed. I know Squick y but It Makes Sense in Context. She is one of the most interesting characters of the book.
- Bolo: Bolos can spend years or decades on the front lines. Of course, they're self-aware tanks armed with a Wave Motion Gun and whatever else the designers could bolt on, so they tend to fight on a larger scale than most examples here.
- In the Malazan Book of the Fallen Whiskeyjack fits this this trope perfectly. Fiddler takes the role in later books.
- In The Black Company series, this trope was written for Croaker and all of the rest of the Company kept in a decades-long magical stasis in the later books, where he also becomes a Four-Star Badass: especially after the Old Guard is resurrected from the magical imprisonment in Water Sleeps.
- Belisarius Series: Valentinian is the best example. There are others who have seen quite a bit of war, but these are often Proud Warrior Race Guy s whereas Valentinian is closer to the classic model of this trope, having a cynical, practical and plebian outlook on war. Flavius Belisarius himself, both in the series and in the real life. He was a Syrian Greek of peasant stock, a bunch that was noted for their practical outlook, and it was repeatedly said that he viewed the war not as an honor or a joy, but as a work that has to be done, which is why he was so good at it.
- Nestor from The Iliad. He's described as having at least a generation on the next oldest soldier present in the battle.
- Colonel Sherman Potter in M*A*S*H. He was a cavalry soldier in WWI.
- The Pacific: Sergeant Elmo "Gunny" Haney of the USMC. One of the leads, Eugene Sledge, wrote a book entitled, With the Old Breed: At Peleliu and Okinawa. Gunny *was* the old breed, having been in the service since the Great War. Victor Davis Hanson noted that he even had a name that sounded like a Marine's name.
- "Old" Snake by the time of Metal Gear Solid 4, although he had everything but the physical age by the time of the first Metal Gear Solid. Old Snake is 42.
- Sten from Dragon Age: Origins acts like this although you never get a grasp of how old he actually is.
- Halo: Sgt. Avery Johnson is at least almost 70 years old in the main trilogy, and has survived about half-a-century's worth of constant frontline combat fighting Insurrectionists, Covenant, and Flood. The fact that he's a Spartan-I probably explains at least part of it.
- Fur Fighters: Roofus Hound fits the bill. He has since retired along with the rest of his squad but this WWII veteran is still out kicking ass with the best of them when Viggo pops up.
- Jolee in Knights of the Old Republic acts like this sometimes.
- William "Bill" Overbeck from Left 4 Dead, a former Green Beret and two-tour Vietnam vet who is the oldest of the original Survivors. While he may not be in peak fighting condition, he still fights just as well as his other teammates, and (from in-game dialogue) is considered to be the mentor of the group.
- Dynasty Warriors: Huang Zhong. Most of his lines invoke his experience and age.
- Carter in Deus Ex.
- In Diablo III the male barbarian is the same Barbarian Hero from the second game in the series, albeit 20 years older and sporting a gray beard.
- Largo from Valkyria Chronicles had served in the First Europan War some twenty years before the game's events, and is one of the older members of Squad 7. It came as no surprise when he initially saw Welkin as little more than a young upstart cashing in on fame.
- The Force Unleashed: General Rahm Kota.
- Zaeed Massani from Mass Effect 2, who is arguably the toughest member of the team aside from Garrus, and of course, Shepard.
- The Regretful Soldier from Echo Bazaar fits quite well. He's always drunk and frequently weeping, but he's still one of the best brawlers there are.
- In Far Cry 2, Josip is 48 years old and a heavy drinker, but still described as a man "who will break you in two."
- Auron from Final Fantasy X.
- James Anderson from Iron Storm.