Plus Painter is a big boy, with proper training and conditioning, he should be able to handle a bigger load than Hamels at the same age.
The key is him using his legs and proper mechanics and not succumbing to the temptation to overthrow and try and blow the ball by hitters, putting excessive strain on his arm. I think the biggest danger for young fireballers is that when they get to the Show, the adrenalin kicks in and instead of focusing on proper mechanics they get enthralled by the radar gun (hot damn, I just hit 100 and blew that guy away!).
The two things working in Painter's favor is he seems to be a "pitcher", not a thrower, even at a young age, and the Phillies utilizing video to analyze pitcher mechanics, which will give them an early warning if he starts to overthrow.