I am good at getting onto and up from the floor. I have made a point of making sure I keep doing it - I do it pretty much every day. As an artist, I often work on the floor and then need to stand up with something in my hands, so I have a hands-free way to get off the floor that works for me.
Sometimes when someone -- often even someone younger than I am -- says "Gee...I wish I could get up off the floor so easily", I feel like saying to them, "Well, why did you stop doing it?" Of course, I never say that. but I am convinced that 90% of people who stop being able to do that, or something else, stopped being able to do it because they stopped doing it in the first place. I keep doing things and therefore keep being able to do them.
This doesn't apply to everything, of course. And it doesn't apply to anyone 100% of the time, either. There are days I cannot get off the floor without grabbing something. If you have a compromised back, as I do, you just cannot shovel dirt to dig a hole for a tree or you are asking for big trouble. But, there are other ways to get something done - it just might take longer. One shovel full a day, maybe. Takes a lot longer, but it can be done. And with most things, if a person keeps doing it, they will continue to be able to do it even if maybe not as easily or as fast or in the same way or as many times.
A famous yoga teacher I studies with many years ago said, "Women can do anything a man can do - they may just have to find a different way to do it." I never forgot that, and I think it's true for everyone, not just for women.
I think people often stop doing something because it's not as comfortable for them to do as it used to be, or as easy. But that's when you need to keep doing it.
P.S. ---this is not a directive to people to "push through the pain", something I never advocate. But to remember that if something becomes more difficult it doesn't necessarily mean you have to give it up completely.