I'm in the same situation but reverse. Sometimes I steal buds from my dad when he leaves it out, but he smokes it every day so he always has alot and he has much more money than me. He knows I take it and doesn't really talk to me about it, he also knows I blaze alot and it doesn't bother him, so idk. As for my son i'd say about 15 is right. I'd teach my son responsible pot use at that age so if he does do it he doesn't turn into one of those kids who fail school and get in trouble with the law on a daily basis.

Added: And I wouldn't let him drink until he moves out. I don't want that shit in my house. Same with chemical drugs and such. Big no no.