Why not try both? And you might want to sit in on an open AA meeting too, over the years I've come to know quite a few Al-Anon's and their children from them coming into the AA meetings I attend.
I thinnk you'll find a wide range of age groups at all meetings. My own experience with Al-Anon is that we had people in their late teens who were regulars. Honestly, I think he'd fit in at either one.
Another program you might check out:
FA Home
I hope you find SR and 12-Step programs to be a source of comfort. Welcome!