IMHO a non-magnum barrel length should be no longer than 24" and 20"-22" is better (24" for a 25-06). The reasons for a long barrel on a shotgun don't really apply to a rifle. A .243 is a great deer hunting cartridge but is a bit limited for larger game. A 7mm-08, .308 Win, 7mm Mauser (7x57), .270, 280 Rem, and 30-06 are great all around cartridges. If you don't reload the .308, .270, and 30-06 may be the best choices. "There's not much you can't fix with a pickup truck and a 30-06."
![Wink ;)](https://www.gboreloaded.com/forums/Smileys/default/wink.gif)
If you have him comfortable with a pump shotgun a Remington 760 or 7600 pump rifle may be the ticket. They can be had in .243, .270, 308 Win, and 30-06 new. Older models can be had in other chamberings. The Remington pumps are great hunting rifles.