RE: Best air rifle ????
Another vote for the RWS-line.
I've got a nice 48-B and I love it. I've killed a possum and a raccoon with mine. One-shot each. It might be a little big for a young guy, but a 45 or 34would be better for him. And make sure you get him a scope that's rated for the reverse-recoil of spring-guns.
I'd stay away from the pump-guns. They're not consistant, and a pain to pump, especially if you're shooting for acouple hours.