I disagree that the 7mm/08 is a more versatile cartridge than the .260 ............both are VERY versatile.
But I do agree that the current offerings of over-the-counter ammo is more suited to a wider selection for the 7mm/08.
You can buy bullet weights (for re-loading) for .264 diameter bullets from 77 to 160 grains that will perform in a .260
Obviously, the twist of the barrel will favor some weights, with the 140 being about the best (same with the 7mm/08 too).
Bottom line is that the .260, 7mm/08 and 25/06....( as well as many others) will serve an up-and-coming and growing hunter for a lifetime. Nothing more than stock adjustments should be required. Look for your best deal on the one your son seems to like best.
)Personally I'd look for a Winchester Model 70 featherweight in 6.5 x 55, but I'm partial to the round!, Not a short action though)