Don't let "he's a small guy" think he needs a small gun. His size has nothing to do with what can HE handle. I'm a small guy (5'6" and 155lbs) and I normally sight in rifles for big guys because they are scared of the rifle's recoil (I tell them to get something they can handle). I own and shoot a double rifle that's legal for elephant and have no problem with it. So, what I recommend is let him shoot different rifles and see what he is comfortable with, then go from there. Anything '06 and up is great for most Big game hunting. If it is just mostly Medium game (deer), most anything legal is fine. My favorite deer getter is the 7mm-08. Low recoil, accurate, light rifle and kills everything I have shot with it, including 2 elk.
WW