If he gets good and wants to upgrade, I would recommend a redline cross bike. The junior program in my previous state got these for all their kids and they raced cross and road on them. Great for kids from 10 up. About the only decent bikes with a large rage of sizes for kids. Heck, get him out racing cross this fall. The chicrosscup needs a lot more juniors.
Anyway, fun times ahead! You just made my day.