I have an older one, too. My DS2, let's call him P, age 34, doesn't shower as often as he should (and then only showers in the evenings, not in the mornings. ) His sweat is particularly pungent, and as he is a teacher, I worry that this will undermine his authority, as the kids may not take him seriously.
I am hoping that his wife is working on it - I have dropped a few hints, and always wash his clothes as soon as he takes them off if he is staying with us.
Once, DS1 and family were to sleep in the same room as DS2 had just vacated, and DiL1 came downstairs with an armful of bedlinen, which I hadn't changed yet. She had taken it off, wrinkling her nose and commenting that it smelt of P!