Well spoken! Let the kid decide later for himself, in the meantime get him something effective that does not kick the stuffing out of him in a light rifle.I started my kids out on 243s but a 6.5 creedmoor or a 7mm-08 would also come into play. Not knowing if kids will grow up and want to handload or not, I'd go with more commonly found rounds like the 3 I listed. Once he is for sure interested, then you can go as wild as you want. I find rounds with lower recoil tend to make younger shooters want to shoot more.
Glad you are getting him started and probably hard to go too far wrong.