Maybe you do need to occupy him. Also, get a filter for your computer if you have one.You can see EVERYTHING he is doing. And see what tv shows he watches. I know it's spying, but don't we want the best for our kids. And, I'm not acussing anything, but if there are things that you or anyone else does in front of him or he hears it, maybe you or they should watch what they're doing.BEST OF LUCK!
I agree with Vance, especially having recently left (or still in, according to some) that stage myself. Staying involved with family, sports, chores, homework, anything and everything. He's young, so he should be doing this anyway.
Biggest suggestion I would make is that in this day and age, make sure he knows your there with advice and support in any situation. Too many parents try to control their kids, but the truth is that they'll find a way to satisfy their curiosity if they don't get answers (sounds like you're doing fine so far if he is that honest with you...). A good read (although a little on the extreme side of possibilities) is generation **** by marty beckerman. Fictional story with a good mix of true stories taken from national newspapers in the last twenty years. Gives you an idea of what kids are dealing with these days. Hope some of this helped.
It is very normal for him to think that way, but he needs to occupy himself with other activities also.