Style in A&P

The first thing that stuck out to me in A&P was the style the author used. The author very clearly shows that this is from the viewpoint of an average teenage boy with his word choice and use of syntax and language. The tone is very informal and adolescent and it is created with the stylistic choice of words. There are a couple examples of similes but each one is very awkwardly worded and sounds inexperienced. Examples are when he describes how they walk as if they were testing the floor and how their minds seemed to buzz like bees. He also uses run-on sentences frequently and it is easy to tell his immaturity level when he describes the 'cat-and-dog-food-breakfast-cereal-macaroni-rice-raisins-seasonings-spreads-spaghetti-soft-drinks-crackers-and-cookies aisle'. It sounds like an actual teenager writing when he later adds in his description of Stokesie that he 'forgot to say' that Stokesie wanted to be manager. Obviously, if the author had forgotten to say that then he could have gone back and added it, so the purpose of it was to add to the 'average teenage' voice. This is clearly a narrative, as it seems as if the boy is telling you this entire story. None of it sounds like an actual formally written novel- it all seems like a teenage boy rambling. He even wants to seem cool and unaffected (like normal teenagers), such as when he says that his parents think that this is the sad point of the story but personally he doesn't. The word choice constantly reminds you who the narrator is. A part that stuck out to me was at the end when he refers to the teenage girls as 'my girls', like he owned them just because he stood up for them without them even asking him too. That reminds me all too well of the self-entitlement that many teenage boys have. 
Contrasting with the rest of the story, I believe the author made a choice to write the last couple sentences in a different style. As the narrator now references Lengel's stiff, dark grey appearance, it seems like it could be a complete different person telling the story. The simile in this sentence (saying that Lengel seemed as if he had just had an injection of iron) sounds completely different from the juvenile sounding 'buzzing like bees'. The author used this stylistic alteration to show the sudden change in the character and how this simple moment actually meant a lot more. This style change also marked an immediate change in tone and mood, though I won't go in depth on that. Did anyone else find any other examples of his style choice and how it affected the story?