The best option would be to get into reloading and load some extremely soft ~115 power factor 9mm with a 147-160 grain bullet using a fast burning powder for him to shoot for fun/practice. I would focus more on the ammo than the gun. You can really adjust the recoil characteristics of a Glock and some other guns by adding weight (frame weight on rail or brass magwell) and changing out the recoil spring for an 11-13# spring to match the lighter power factor ammo.