I’ve got the 6 in glock and 6 in TRP as well
Also an ar rifle in 10 mm it screams but have never cronied it
Throws brass a mile so I put on a A2 stock and a rifle buffer with all tungsten weights so I can find my brass
I have another complete 10 mm 16 in to put together if I keep it
Bought my son year years ago a youth Remington model 7 in 7-08
Nice size for him in his early teens
As mentioned you can get reduced recoil ammo for it or down load it if you reload
Then you can try the full power loads and see how he does
A good replacement recoil pad makes a difference as well