This certainly won't be his only hunting rifle and I had planned on getting him a .44 mag since I shot a rossi break barrel not too long ago and absolutely loved it and the accuracy was second to none for such a heavy round I personally placed groups in a nickle at 100 yards with that rifle and a Nikon buckmaster and the recoil was nothing, unfortunately life happens and I sold that rifle now I wanted to get him a lever action .44 mag but I've never shot one and I can't compare the recoil to the single shot I had but all of that is later down the road. bobjones223 you've got me very intrigued with the 45 LC now so I will certainly look into that more, possibly even for the both of us in the future.
As stated above, .243, 6.5 Gren, .300 BO or even a 6.5 Creedmore. All are lower recoil. The AR platform is a good idea also. You can build a lower with him and buy an upper in the caliber of your choice. Get a 5.56 upper for cheap practice and getting him familiar with different shooting positions. You can have a bunch of different uppers to choose from. (6.5 Creedmore and the .243 would be on the AR 10 platform as the others are on the AR15 platform)
There is one more I'll throw out there. The new .350 Legend. It doesn't have quite the range of the ones listed above but for closer work, under say 200 yards, it is a viable option.