of the three choices you posted (7RemMag, 300 mag, 7mmwsm), I'd go with the 300 WinMag..... like was said earlier, you can load it up with reduced recoil cartridges (believe Remington loads them for the 300). Plus, it'll last him until he's an old man and will do him for pretty much anything he wants to hunt.

That being said... nothing wrong with your other two listings or even a 7mm-08, 308, or 30/06 if you opt out of the magnum range.