On the washing and underwear fronts, it's amazing what a young body can put up with. I speak here from personal experience as a seriously scuzzy git! I'm mostly cured now, since I've found it's more comfortable to wear clean undies, but at uni I was infamous for my shortage of underwear and frequent reuse of same, and for my use of swimming trunks when I'd forgotten to wash the few pairs of undies I did possess.

Bottom line, if he doesn't smell (too much) then don't worry. And if he really starts to hum, you can bet his friends will get him to wash! Or he'll start to itch and get spots, and then he'll figure it out for himself.

A grunt is usually a acknowledgement you're there, and is used by all males regardless of age. Whether it's good ("Hi mum") or bad ("you're in my way") is difficult to tell. Read Pratchett and consider the word "ook".

Graham.