In Salinger's The Catcher in the Rye, what are 3 characteristics that show Holden being a good representation of a teenager?

The most striking characteristic of Holden Caulfield which makes him seem a good representation of a teenager is his use of language. This is evident in the very first sentence of the novel.

If you really want to hear about it, the first thing you'll probably want to know is where I was born, and what my lousy childhood was like, and how my parents were occupied and all before they had me, and all that David Copperfield kind of crap, but I don't feel like going into it, if you want to know the truth.

Here is another good example at the start of Chapter 12:

The cab I had was a real old one that smelled like someone'd just tossed his cookies in it.

He uses slang, profanity, hyperbole, sarcasm, and bad grammar. He affects a tone of boredom. He is obviously a bit of a rebel, subject to swings of mood and possessing other adolescent traits. Salinger has done a remarkable job of making this first-person narrator sound like a teenager, just as Mark Twain did a remarkable job of making Huckleberry Finn sound like a smart but uneducated youngster who is about thirteen or fourteen years old.

Another teenage characteristic of Holden Caulfield is his apparent search for an identity. He is always trying out various roles. He doesn't know who he is, or whether he is a kid or an adult. Holden wants his freedom, but he doesn't know what to do with it. He tries to order alcoholic drinks although he is only sixteen. He tells various people he is in his twenties, and nobody believes him.

Well, youth is the period of assumed personalities and disguises. It is the time of the sincerely insincere.
                                                                   V. S. Pritchett

A third teenage characteristic which is hard to overlook is Holden's interest in sex. Although there are no sex scenes in the entire novel, there are many references to girls. He tries calling one girl in the middle of the night. He keeps thinking about Jane Gallagher. He has a date with Sally Hayes. In Chapter 10 he picks up three girls from Seattle who are much older than he is. He keeps thinking about Jane Gallagher. At the start of Chapter 17 he is fascinated by all the girls in the lobby of the Biltmore Hotel.

A lot of schools were home for vacation already, and there were about a million girls sitting and standing around waiting for their dates to show up. Girls with their legs crossed, girls with their legs not crossed, girls with terrific legs, girls with lousy legs, girls that looked like swell girls, girls that looked like they'd be bitches if you knew them. It was really nice sightseeing, if you know what I mean.

His interest in sex gets him into trouble in Chapters 13 and 14, when he accepts Maurice's offer to send a girl up to his hotel room in what may be the best and funniest as well as saddest scene in the novel. Holden is trying to be "suave as hell," but he can't perform with Sunny and ends up paying twice the usual fee for a "throw" without getting thrown. He confesses to the reader that he is a virgin--something he would never confess to any of the boys at the three schools that have expelled him.

There are other teenage characteristics throughout the novel, such as loneliness, self-pity, existential angst, and curiosity about the world. But almost all his teenage traits are revealed or reflected in his use of language. Salinger convinces the reader that this is a real teenage boy writing the novel; and many readers ask questions about Holden which show they think he is not only a good representation of a teenager but a real person., a real teenager. This is a great achievement for a creative writer. It probably explains why The Catcher in the Rye has been such a phenomenal success. Many people who discovered Holden Caulfield when they were young are now teaching English classes and assigning The Catcher in the Rye to their students. It is a great American classic.