I would not worry about the break, if he can handle a 20 gauge slug. I was out with my nephew this weekend, his first time out. He was shooting a 2506 which should recoil similar to the 7mm08. I shot it a couple of times and it was quite mild. He shot my 300 WSM without a problem. The biggest issue would be to get a gun that fits him well. If he struggles to handle the rifle cause it does not fit him, the recoil will be amplified a bit. Also, buy a bunch of cheap ammo, nail some apples to a board and let him practice.

BTW: I have an 11-87 in a 20 gauge w/ a rifled barrel shooting 273gr. sabots. I think it kicks harder than my 300WSM.