I hesitate to say this out loud, but mid-50s and nothing hurts yet, except the migraines I've gotten since teenage years.
Knees last if you take care of them. Back lasts if you take care of it and are lucky, and don't get fat, and are lucky, and don't work a physical job, and are lucky.
The more active you are, the greater the likelihood that you'll sustain serious injuries at some point. Those injuries go on to become chronic pain as you get older. I was very athletic and very active when I was younger, and I feel it now. I'm still active, and staying active helps those old injuries to hurt less, but they still always hurt.
You mean me doing karate 3 times a week which has given me a cracked rib, a herniated disc and countless of bruises and minor injuries might leave me with chronic pain? I don't believe you!
Heh, coincidentally, many of my injuries are from Kung Fu. Many more are from riding dirt bikes, and the rest are from recklessness or just plain accidents. Surprisingly I have no lasting injuries from soccer, baseball, football, track, cross-country, rock climbing, or outdoorsmanship. I guess organized sports are a little safer than more extreme sports.