Wait. He traveled back 23 years in the past, which means even assuming they're in their last year of school and that they're 18 right now, the oldest he could be is 41. Maybe I'm just misunderstanding what constitutes an "old man", but that's really not that old is it? I know plenty of guys that age still running marathons and doing martial arts. And he already threw out his back a few times and walks with a slight hunch? Did this guy just not take care of his body at all, or is the 23 years just a mistake on the author's part?
Don't get me wrong, I'm all aboard and this looks charming enough, but the discrepancy between the age he supposedly was and the mannerisms he's showing is just really throwing me off.