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...
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...)