I totally agree with you on old being a state of mind. I have friends who are in their 40's and 50's and act like they are 70. In my line of work ( I drive a tour bus) I meet many seniors and get a lot of" I am slow because of pick one: Knee , Hip, replacement." The general theme seems to be if you don't use it you will lose it.Even within these seniors there are young and old depending on their thinking. I met one who comes to mind who at 84 years young was still running 10 k runs and he did not take up the sport until 65. I honestly believe that a lot of these folks would not be on canes or the medications if they were more active.The good thing about dealing with this day in and day out is that it motivates me to stay active because I don't want to end up with that quality of life.
On the positive side I do notice an increase in a more positive mindset over say 15 years ago amongst the 60 + set and this is a good thing. People like yourself setting an example I think inspires others to try, so keep setting a positive example and you never know some day that van will stay parked.