Peeping is normal childhood behavior. Sexual abuse isn't. I understand why you would think this person is dangerous, and you may be right. But if he hasn't done anything illegal, don't blame the young man for what his father did. That doesn't mean you shouldn't keep your family away from him, but do it as a precaution, not an assumption of guilt. He could still be a decent guy.<br />
As for your question, there are certainly some predispositions towards deviant behavior that are genetic. Testosterone levels increase sex drive in males, and that is certainly hereditary. But there are also things that are perfectly innocent naturally, but society has taught us not to do. Children have no problem running around naked until taught not to. More than likely he just wasn't taught. But whether it is nature or nurture doesn't really matter, a person shouldn't be blamed by the way they were born or the way they were raised. <br />
Someone (you) needs to tell him what happened to you. Certainly his parents aren't going to do it. If he never learns the effects of this type of behavior the cycle may never be broken. Maybe he does have a problem, but he cannot seek help if he doesn't know it. But hopefully this is simply a bit of (justified) paranoia on your part.
In this cause, what you are describing is a "learned behavior" from watching the actions of his father. I would try and avoid this person from now on, sounds like they are on a very dangerous course.
So we're talking about an attractive woman in her late twenties with a teenage boy in the house. I can't answer your question but he just sounds Male to me.