Well, at 14 it's not like he can drive himself anywhere so you have control over where they go, that's good. I think if you're too strict it bites you in the end. I knew girls who got pregnant BEFORE they were allowed to date
I think communication is the best, and letting him know that you trust him.
I have two boys that aren't there yet but have started puberty. I had that uncomfortable talk about puberty and sex stuff with them because I wanted them to know that body changes are normal, liking the opposite sex is normal and that I've always felt only people in love have sex. Anytime someone has sex they risk bringing another life into the world and why would you do that with someone you don't love?
Kuddo's to you for having a son that trusts you enough to ask and for getting good grades.