i have a 13 year old son so i think I know what you are going thru.
My son is also a very nice boy and not one of the "mature" kids in his grade level. We talk very openely and honestly about anything really but I've always tried to explain things about sex and puberty and that kind of stuff so that he knew he could come to me and for the most part I think he does. Sometimes there are some things I wish he wouldn't ask!
Well, not really, I just wish they were things he hadn't heard on the bus and wanted to know what they meant! Anyways, so far our rule has been that he could go on "group" dates. In other words, if he wanted to go to the movies with a few friends and that special girl that would be fine. Or to friendly's for ice cream sundaes or something like that. This really hasn't come up yet but there is a girl he likes at school but he can barely say "hi". As he gets older and things change so quickly now, we might have to modify that and play it by ear but that's what we say now. Good luck whatever you decide!!