My vote is for anything in the .308 Win family (.243, 7mm-08, .308). I bought a 7mm-08 for my wife, who is only about 125 pounds, and she handles it really well even when shooting 140 grain Partitions at 2800 fps. We put a Nikon Pro-Staff 3-9x with the BDC reticle on it and the aiming points are almost spot on out to 400 yards.
In the same vein as DallanC, he can shoot now and still grow into a heavier load for either 7mm-08 or the .308 (very little difference in recoil if you use 150 grain bullets in the .308).
On the other hand, if you don't hunt elk for some reason, the .243 is a good round for deer and can be better suited for predator/varmint shooting than the larger, harder recoiling rounds.