Not trying to restart a 'caliber wars' battle . . .
There's an old saying among engineers that goes something like:
"If you put n number of people into a conference room to solve a particular problem, you will invariably get n+1 opinions on how to solve it".
I think the suggestions regarding the 7mm-08 are probably good advice, although I admit I have never shot one. With that in mind I recognize that my opinion doesn't count for much on that topic.
I have shot a hog with a .223 using an AR-15. I only used it once. Immediately afterwards I bought a Bushmaster ORC in .308 (effectively an AR-10) which is what I now use. I've shot a dozen or so hogs with .30 caliber rifles and I just like the extra hitting power.
So the folks who like to use .223's on hogs, and who have good enough aim to put the bullet where it needs to go should keep using them. Me, I'm not such a good shooter (only qualified as Sharpshooter in the Army
) so I go with the larger caliber. That's my story and I'm sticking with it.
The point of all this (if there is one) is to say that if you're going to be sharing this rifle with your son, you obviously want a compromise between what he can handle now and what he might want later. Another option would be to get a rifle for which managed-recoil ammunition is available --
http://www.chuckhawks.com/rem_managed_recoil.htm Later, when he's ready, he can start using higher powered ammo.