That's horrible. I'm assuming someone else was using the gun improperly, I'm having a hard time imagining how you'd wound yourself in the arm and torso if you yourself were shooting the gun.
Hope he recovers quick, he's still young so I'm sure after the shock wears off he'll bounce back in no time. I swear before I hit my teenage years I was invincible. I could fall down hills (rocky, tree strewn, snake filled hills....and I fought a bear when I was only 3), get hit in the face with just about anything, go flying off my bike without a helmet and get up without much more than a scratch. Now it seems every time I stub my toe I break the damn thing, I'm only in my twenties, I'm dreading hitting 30.