Be sure your son and all his friends use paintball approved goggles/masks. It's a thing many new players getting into it overlook, but very important. I can't count how many times I would have been hit in the eyes had I not been wearing my goggles. $20 at WalMart is a small price to pay to keep one's eyesight.
I think the gun was a good choice. Simple to shoot and easy to maintain. Yes, he might be outgunned occasionally (if they play with semiautomatics), but he will get better because of it. If he complains, tell him it will build character and that if he wants to save and work to get a "better" one, at least you gave him a chance to get started.
He can always come here for help and tips, most of us are more than willing to help a friend.
I got started in paintball in much the same way. I have a rather large family (cousins, etc.). One day a few years back during a group camping trip, we decided that we could do paintball as a family get-together. I started with a package that costed $200 including air tank and balls, mask, loader, and gun.
Some lost interest, but it never stopped with me. I still play, harder than ever, I've also saved up for many different markers over the years. What you've got sounds like a goood thing.