As others have said, it would be best to start him out with something like a .22LR, or even a .410 shotgun! At about your brothers age, my dad started me out with a single-shot 12GA. My flinching problem took a few years to get over!!!! Flinching is a hard habit to break, and it never really needs to be started in the first place! Most people can learn to shoot some pretty hard kickers, but it helps to start out small, and work your way up! Good luck!