I assumed the joke was that as you get older things are just more stiff and you don’t recover as fast. Yeah, it can be reduced with more exercise/activity but you’re still getting older.
There was an event where this became apparent for me. I played softball for years in my 20s. Stopped for a bit and returned in my 30s. I was actually in better shape when I returned. One day mid-season, I was rounding first base, not even particularly fast, and I felt something tweek. By the end of the day I was stuck on the couch and could barely move. I had to take the next day off.
I don’t think that’s what the meme is saying, it really shouldn’t need interpretation. However, I agree with the rest of what you said. Youth gets strength, endurance, and faster recovery. If you’re older, you can still hold on to strength, but endurance and recovery take hits with time.
