I ran a triathlon in my mid 40’s. Came in a respectable middle of the pack but I realized the next year I’d move up an age group and I imagined I’d really beat up on those old geezers. Came in 2nd to last. Any random 40 year old can work themselves into shape to run a triathlon in a few weeks time but if you’re still doing it at 50, you’re a more or less serious athlete. So much easier to stay in shape than get in shape.