Yeah, it's weird (context: I'm older than 13, but younger than 18). I contacted support about it, and the requirement is that you have to be 18 or older, regardless of where you live. Logic seems really weird, but that's apparently how it is.
You CAN however, change the age of his account by making yourself the owner (and all of its necessary details, etc), then requesting an age change through the in-game help. You'll be asked to post a form of ID to verify your age. After that, boom, your son can enjoy the free stuff.
(Also, congrats to him for almost getting his first GL. A big milestone, and I find it an impressive feat for someone that young.)
Edit: meant to say that it's a possibility but I made it seem like a guarantee. Whoops.
