Well regardless of how old you might think someone else is, if part of your job or your alloted duty requires you to perform ID checks, then it should be done. It should be routine in fact. I'm talking in general here, not aimed at anyone, but it's all part of the preserving the state of whatever institution, or in this case sport, you're working for.
The point is to not give the general public or overseers any ammunition to come after us. It sounds like George is a good dude but the bullet was chambered when he sold the gun without checking for ID. It could've gotten him in trouble if the kid was stupid. But at least he's taken measures to rectify the situation.
Those guys that others mentioned (the bar guys and stuff), they don't even care and bend rules the way they see fit, even if the crime doesn't warrant a severe punishment. But ammunition is there for the powers that be to serve any sort of punishment they see fit.
"May you fight with the strength of ten full grown men."