Yeah.... but you know what's most damaging when you get older? Sit-ups. Trashes your hip flexors. Knees happen regardless with ruck marches and parachute jumps, but load bearing equipment and pointless sit ups will grind up your pelvis.
I do some other ab stuff. No more sit ups for me. I'm surprised for the years I did them I didn't have hip issues.
Still hit the gym two or three times a week. After working out for 40 years I don't ever see myself not doing it.