Age is a mindset in the same way suffocating is. You may feel as if you're suffocating when you are not, but if you are suffocating, you are suffocating even if you don't realize it.
The way you put it is the closest I've found to my opinion. I mean, it's definitely not just a mindset when you realize you can't run as you did when you were 20 and played football, but maybe you haven't even noticed cause you haven't played football since your 20s. If it is a mindset, it's one that heavily depends on the moment.
I'm 52. I still play football. But now I cover the slowest opposing player, not the fastest.
My approach has been that I'll keep doing things until my body proves to me that I can't. It has started doing so. You can ignore age longer than many people think, but not forever...
If my body responds like yours, I still have a good three decades of activity. I can live with that. But yeah, as long as you keep a strong mind I suppose you can get over the limitations, that's until your body collapses.
Keep using it. You can't just wake up in three decades and decide that you should still be able to be active. You have to keep using it week after week, year after year.
Find something you like to do. Do it regularly. You can keep getting better (more skilled even if not faster) for a long time.
Sometimes you'll get an injury. Rehab it, and get back to doing whatever it was that you enjoyed. It may take a year to get back to where you were. It may hurt. Do it anyway. Do what you don't want to have to do for a year (if it takes that long), so that you can do what you want for several decades.
That all said, know your limits. If you try to crash through them, bad things happen. (I still remember the lecture from that one physical therapist...)
