Wild Things: YA Grown-Up discussion

These posts look great, they just look older so I'm not sure if parents are still commenting. I have a 12 year old son who reads like crazy. He mostly likes action adventure types like Rangers Apprentice, but my questions is eventually, with what they see on tv and in movies, a simple book like this isn't going to hold their attention. Obviously I don't want him reading books with graphic violence and sex, but how many killing in a book are too many?