I'd certainly say one of the .308 versions.....

years ago when I was youngster I remember my .270 feeling like a cannon. I want to say I was probably 5' 100lbs ish.

I think a .243 with a premium bullet on deer would be plenty lethal, minimal kick/ideal, and a perfect antelope rifle too. Otherwise I'd consider the 7mm-08

Get a .243, you and him both won't regret it.