Well, it is also confirmed that the harder you work, the harder your body is working, so that is not good for an old person. I am not saying you are , but when you get to be old, play a board game or play cricket. How do you play cricket ?
I am old from your viewpoint. 54. But, most people have trouble keeping up with me. I believe differently. I have noticed that when people retire they sometimes start to relax and rapidly become dead. My belief is that as long as I keep going and doing things that I find hard, I'll be able to do them.
A couple of years ago, I had a bad reaction to some treatment for an old injury. (Found out I'm allergic to aspirin). The upshot of it was that it damaged my heart quite badly. I was being told to "take things easy" and so on. But on the second day, I got up out of the hospital bed and walked around the outside of the hospital. Did about a mile. Six weeks later, I went on a 12 mile charity walk and raised two thousand pounds for a cancer charity. Now, no-one would know I have a damaged heart. My specialist says he's never know anyone recover so fast or so well. And I have Type I diabetes, which makes it even more incredible.
So, don't relax. Keep pushing harder and do things that you think you can't!