Well, I always say "You're only as old as the man you feel"... (which was a great line when I turned 25 and I was living with a 20-year-old.)
"I bet you've got the body of a man half your age."
I still have the same body as I did 50 years ago in high school (still wear the same size clothes) although i'm not quite as quick as I was at 40 but can still outwork 80% of them.
Even in the 40 years that I owned and ran a construction company I never gave up working physically. Since I closed the company I don't put in 12 hours a day 6 days a week any more, I cut it back to 8 or 9 hours 6 or 7 days a week.