Atleast he knows he good at something. At that age a lot of kids have no idea which way they're going. I know I didn't.
As far as starting a band I always hit up the different high schools in our area's school bands, those kids usually play instruments besides the ones they do for their school band. I also go to local places that give lessons, and just ask an instructor. Just keep an eye out, and you should be able to find people.