Glad to hear you ar vbetter. The gym routine at 81, is impressive!
Gym routine was not easy when I began at age 75 after quitting golf. If you start gradually doing a little more every month, I am impressed how our bodies can adapt.
If I can maintain the discipline of dragging my butt to the Gym every evening, I see no reason why I should not feel the same energy at 90 or even 100. Fortunately the private community gym is an easy 5 minute walk from home and I go after 9 pm to avoid crowds. Usually I am the only one there.