That'll work. I know all mine were chomping at the bit to deer hunt with pappy. If yours is anything like mine, that will put a mindset in him to "get over it" pretty quick too. I got a pair of twin grandsons I'm working with now (I pity their mom and DAMN I'm glad we never had twins) that have zero fear but they aint retarded either. They always want to see papaw shoot it first to make sure it wont knock them on their butts
I guess their daddy warned them
Just work him into shooting that 7mm-08. Show him it doesn't kick as bad as that 20 gauge. Good luck to ya. Kids can be one of the most stubborn beings on this planet! Even after they are all grown up!