One would think that as you age you carry on as normal but this is not so. Many people develop foot and leg problems that prevent activities and some become quite immobile. In my case the pads benefit my feet have faded away and it is like walking on rocks if I am not wearing the right shoes. This is something my father and brother have also had problems with so it may be genetic as well as age related.
In my elder sister's case she has problems with her knees. That led to one replacement and the other that should have replaced has been put off. The effect is that she has little feeling in the joint and managed to fall heavily while swinging herself around. It put her in hospital for three weeks while a pin was inserted to help the broken femur repair itself.
While many older people are facing hip and knee replacements there is stories that maybe the bones are unable to last out the distance. We have, after all, gone by our use by date, which some claim is around 70 years.
This seems to have effects on other parts of the body as well. Although the rest of me is holding up rather well my attendance at a gym helps keep me fit. Half an hour on the bike is enough and then a walk around the local lake gives me extra exercise. There are also weight and stretching machines that are used as well as PT classes for heart and cardio health.
If one can keep up the pace of moving instead of sitting, then things like immobility should be avoided. It depends on the individual how far they want to push themselves, however, as many think they need to vegetate in the senior years to make up for all the times they had to labor when younger. That may sound like a good principle but it is devastating for the feet and other body parts.