Before My Time

Funny thing. This Wiki has entries relating to The Maltese Falcon, Sherlock Holmes, and many, many connected to William Shakespeare. Does this mean that a large number of Tropers are Really Seven Hundred Years Old? Probably not. More likely, their education and particular interests have left them with knowledge of things that happened well before they were born.

The opposite is often true of people - and especially young people - in fiction. Barring special circumstances, characters will be limited in knowledge of movies, music, politics etc. to things occurring after their birth. In some cases, the ignorance extends to some time after they reached high school.

Before My Time is a kind of in-universe version of the Fleeting Demographic Rule, wherein a character demonstrates glaring ignorance of anything significantly in the past. Frequently this involves blank stares and crickets chirping in response to something said by an older character.

Sometimes inverted wherein an older character will beg off or dismiss a phenomenon as "after my time."

A more technologically-oriented version of this is What Are Records?

Examples of Before My Time include:

Film

In Monster-in-Law, Jane Fonda is a newscaster interviewing a "dumb blonde" type famous pop singer, who mentioned that she liked really old movies, and gives some examples, none of which are more than ten or fifteen years old.

Live Action TV

Sometimes seen on The Office. In one episode, Michael goes clubbing with Ryan and chats up a girl with a tangent on Back to The Future. She doesn't seem to have heard of it, even though the movie or one of its sequels is basically always playing on some cable channel or other.
On House, the title character is making one of his trademark analogies to Thirteen, in this case referencing Altered States. She tries to shut him down by saying the movie came out before she was even born. Which apparently prevents her not only from having seen the movie, but also from understanding anything he says about it. Just in case you were wondering why fandom so loves this character.
On The X-Files, Mulder goes to interview a retired FBI agent who investigated X-Files in The Fifties. The agent asks Mulder whether he's heard of the House Un-American Activities Committee, but immediately assumes that he hasn't. Even if he knew nothing about Mulder personally, the topic is covered in high school history classes.
As the youngest character on Thirty Rock, Cerie continuously fails to recognize references to anything from earlier than last month. This does fit her character as she is a Dumb Blonde.
The "after my time" inversion was used in those exact words on Lost when Locke doesn't recognize Sawyer's reference to Of Mice and Men. Since Locke is actually the Smoke Monster, who's been on the Island for centuries it kind of is.
- And then it's played straight in season 5 when Sun asks Ben where the rest of the mysterious statue went. Ben says "it was like that when I got here."
On Community, one of the characters in a community college study group makes a reference to Sam and Dianne.

Annie: Who are Sam and Dianne?
Shirley: Ok, we get it! You're young!
(And must have grown up without a TV, given that it's been in syndication her entire life.)

Music

From Simon and Garfunkel, "A Simple Desultory Philippic":

When you say Dylan, he thinks you're talking about Dylan Thomas
Whoever he was
The man ain't got no culture

Newspaper Comics

Played straight and subverted in The Boondocks. The Freemans' neighbor asks Huey whether he's named after Huey Lewis, and Huey actually responds, "Before my time." The subversion comes in the fact that Huey has just given an erudite lecture on Black Panther Huey Newton. He may just be baiting the poor guy.
Inverted possibly to excess in 9 Chickweed Lane. The post-adolescent characters frequently speak in pulp detective slang and reference old movies like Casablanca, but seldom talk about contemporary culture. Of course, Juilliard arts majors can be a little eccentric.