I'm 6'-4" 215 lb... haven't really had "size" be a problem with backpacking. My 1-person tent is about maxed out as far as length... and my Marmot bag is about all the narrower it could be... but stuff still works fine.
That type of camping isn't for everyone. My elk buddy calls it "cold camping" as opposed to wall tents with wood stoves and so on. But man does it open up some country. Just put it to him this way. Normally he hunts X far into the woods. Now imagine that you pack in X far instead, and THAT is now your starting point for the hunt. It's like X + X = ELK! The algebra is hard to argue with <g>.
Just don't let him over-pack. Nothing will kill a budding backpacker's interest faster. If I were taking him in his first time I'd secretly steal away some of the shared gear and make MY pack heavier. I know it's not gonna ruin it for me, I'll just suffer a bit more, but the extra 10 lbs or whatever might make a tangible difference for a first-timer.
