You don't stop playing when you get old. You get old when you stop playing.....
Precisely. I am 62 and took up hapkido a couple of years back with my son. For him it was for discipline and self defence for me it's to regain flexibility and agility. Seems to help with both surfing and MTB and helps me maintain my mediocrity. I use riding to gain fitness and endurance for the gradings - which are pretty tough.
So even though I may not be riding as aggressively or skillfully as I might have, I'm still getting something out of it. Although I did manage to get into the top 10 in Strava for one of my local loops in the last year, but only 1! Then there are the occasions where I discover a new trail and it's like being young all over again! I don't ride road much these days, the princes highway used to be very quiet 30 years ago now at 5am it is peak hour with all the new housing development on the south coast.
I also undertook and completed my surf lifesaving bronze in February and while I wouldn't say it was arduous there are some times you must meet, swim 400m in under 9 minutes and do a 200m x 200m x 200m run/swim/run in under 8 minutes. I have to say I was happy to beat the teenagers I was training with and came first every time! It's a small club, it certainly wouldn't happen at one of the big clubs or any of the Cronulla clubs but I felt smug for a day or 3
Never stop physically challenging yourself.