Different children can handle more adult themes than others. How do you tell them apart? I taught my kids about sex rather early on, just as I taught them how to drive safe before they ever got behind the wheel. Now my kids are adults, have good lives, careers and I have two granddaughters. I never told them they couldn't read a book they wanted to read.
The worst behavior I saw in my kid he learned from other kids in school. I had to explain to him why his opinion based on other kids was wrong. And he even already knew it was wrong, but peer pressure is a hellva drug.