His face doesn't look 48, so it's not hard to believe that his body would match his face. Nobody knows what 1000 pushups and 2000 sit-ups per day would do for the body, because I'm sure no one other than Herschel has ever sustained this routine.
I am not bashing you in the least, but do you really believe:
1) that Herschel has sustained this routine from the age of 15; and/or
2) that he ever actually did this routine?
There were a set of twins that played doubles tennis for a while that blatantly lied about their workout routines, specifically the amount of pushups and situps they did per day. I played high level tennis, and had the chance to speak to someone that trained with them for much of their early years, and was told that they were always liars, about everything.
So, who really knows?
I must admit that Herschel, on or not, is a specimen at the end of the bell curve.