The hot potato in the book blogosphere at the moment is that Wall Street Journal article on Young Adult fiction. I don't read a lot of YA books now and I didn't read ANY when I was a teen. I read adult books. I do remember writing a Standard Grade dissertation on Trainspotting (I would have been 14 or 15) and it didn't disturb me or turn me into a junkie. If anything, it will have put me right off a life of crime and drugs if I'd been so inclined.
I also remember reading a lot of Dick Francis, where people get killed or attacked on a regular basis, and the occasional Stephen King. I also read plenty of books with sex in and I managed not to get myself pregnant. Shock horror!
The thing is, books don't have ratings like films. Just because a book is aimed at one age doesn't mean there are any restrictions to it other than what parents allow. If we start adding certificates to books, what on earth will kids study in school? Romeo and Juliet is all about civil war, murder and suicide, do we stop teenagers studying it? Let's face it, R&J was the original YA read, two teenage lovers getting in a pickle (Juliet was only 14).