If it were me, I'd start with a .22 pistol or carbine (perhaps a Ruger 22/45 Lite or 10/22 carbine just because of the "go fast" stuff you can do to them if you choose) and I'd get him involved initially in steel challenge type games just because they don't require stage planning and movement and also don't require working from a holster. If he remains interested and has a desire, you can always jump to the run-and-gun games.