I think you've got to give your son a little more credit. Just because he may be young, doesn't mean that he doesn't know "how to stop." I can certainly appreciate where you're coming from, but if your son is going to engage in any sexual activity with a girl of his choice, he's going to do it whether or not you put an age restriction on his dating. If his friends have house parties, he can easily enough sneak off with his girlfriend. If his friends go to the movies, he can easily get time alone with her. And I'm not saying that you should stop him from doing any of those things with his friends by any means, just that he is a teenager, and they do have a mind of their own. I wasn't even a rebellious teenager, but when my mom started restricting who I could hang out with, i sure did my darnest to do the exact opposite.

I think that no matter what you decide to do, its important that you talk with him, and explain to him what exactly it is your trying to say here. I think he'd be more inclined to listen to you that way, then by placing any age limit.

I'm not trying to offend anyone, or tell you how to treat your son.. I just wanted to put in my two cents, and i'm sorry if it bothers anyone.