The first sentence of the novel makes it clear that he is basically talking to a therapist.

From this fact, we learn that there are 2 Holdens in the book: 1 who is younger and is the person who is did the actions (leaving school, going to NYC, etc.), and 1 who is a year older who is narrating the novel to the therapist, which is a narration of the events in his life from a year prior. And thus he is an unreliable narrator.

So it’s fascinating that we are watching the events of Holden from the perspective and diction of an older, post-consciousness-shift Holden, which we don’t see/hear happen until toward the end of the novel.

I didn’t catch that so much when I read the novel for high school, but when I picked it up again after college, it clicked for me and I loved the writing style/choices that Salinger managed to pull off.