Though aging surely plays a role, I know I hadn’t realized just how much muscle strength I had lost while I waited for surgery (4 years in all thanks to CoVid). Between the wait and related deterioration as I was able to walk and do less and became more reliant on a Walker and cane, and then the recovery required post-surgery after all the cutting and stretching of muscles and ligaments, etc. I’m still a long way from having good muscle stamina. An exercise therapist helped me to understand that and assured me it would come if I was willing to work at it. But she did say it would probably take a year. I do find it improving with the exercises but I couldn’t do 2.5 hrs of walking at a street fair. (I’d take my Walker to such an event so I could rest as needed and would be able to enjoy it more that way). I even find a significant difference by the end of the day by which my legs are tired and have much less strength. So it sounds like you’re doing well (at least by my standards 🙂 and I have confidence that, if we keep working at it, we will see continued improvement.