I saw your comment in the other thread, and it was interesting because only today I read an article in the newspaper about how, in a strange reversal of roles, American parents were kicking up a fuss about how very violent this movie was and how their kids shouldn't be watching it, while parents around here apparently didn't care so much.

I don't think any book is considered YA exclusively because its characters are teenagers. Or even primarily. Of course nearly all YA books have teenager characters, but it's the writing and the marketing that make a book YA or not.