I still think he should do some cardio...I wouldn't be surprised if he lost some of it. I agree with doppel here...plenty of guys that aren't tone and don't work out there bodies will store fat in there pecs. I don't think 5'11 170lbs is necessarily "skinny." It's more along the lines of normal. Either way cardio never hurt when it came to toning up all around. Go see a doctor anyways.
The chart here says he's just above average weight:
[url]http://www.disabled-world.com/artman/publish/height_weight.shtml[/url]
5'11 at 170 would be above target for his age. Hell I'm 2 inches shorter than you and almost 40lbs lighter than you...so. Hell, I'm skinny so I'm not even on the chart, lol...132-135lbs, 5'9" @20, lol. But I'm a bit of a cardio freak.
I think he should post up a full body picture of himself to see how proportional his body is. You don't have to show your face if you're worried about that.