20 gauge is best for the same reasons listed above you can do anything with a 20 guage and also when he gets older and has a house and family of his own he has a defense shotgun for himself and he can pass it down to his kids 410 is a good round but not for deer or turkeys really anything else but squirrels and rabbits and other small critters like that i would take a 20 ga or a 22lr that way you can teach him precision shooting to