I got my girl a 20, youth model that will kick the snot out of even me every time I shoot it. It's brutal, right up there with my 12. Find a 20 and 12 and let him try them both. Stay away from 3" mags for a while, make sure he has on a heavy coat for padding when practicing. Stay away from single shots until you're sure he can hold onto a gun when it fires. The hammers on singles are in a very dangerous place when the gun recoils all the way up and back.