Given that he's a top 600 player (which he is) and he is younger then I, then I would give him a 6.0, weak 6.5. Even better, I would almost classify him as an actual pro (don't know if he's gone pro or if he's gonna play college...).
Voila! 6.5 it is, though it will go up to 7.0 in the next few years (the rating system is so stupid, remind me never to get into one of these USTA rating threads...).