Don't have time to read the whole thread, but yes, I know I'm getting old and a lot of stuff is not as easy to do as it used to be. That said, I still do lots of stuff most folks my age cannot do, so I will offer some advice (take it or leave it).
I used to do biathlons (running/biking) but started to feel less competitive when I turned 60. Back issues in the late 60s and early 70 created more obstacles.
PT, exercises, and eating right and controlling your weight are all very important. When I hear someone say they "inherited" an issue, I can usually find the reason for it in their refrigerator. More often than not, it is not genes, it is dietary and exercise habits that have been inherited. The older you get, the tougher it is to change, but it can be done. Never give up, always listen to your body, try to stay off all drugs (they all have side effects, and as a nation we have become dependent upon them). I get on the scale every morning, so I don't let my weight "get away from me". I'm 6'1" and I keep my weight between 180 and 190 lbs. Control portions, carbs and sugars. Eat plenty of fruits, vegetables and nuts, and I love my venison steaks and chunks (I don't process any of it).
That said, I needed to take Aleve for a while to help my recovery but got off it as soon as I could.
I do a 20-minute exercise routine every morning to help me function (stretching and then strength) focusing on my core (for the back), my knees and my neck (hurt it when wrestling in college). If I don't exercise it, arthritis will tighten it up. If I do not do the exercises, my left knee will bother me, with the exercises I don't notice it at all, and I drive a Mustang with a clutch! (was very heavy duty, but I upgraded to dual disc).
I still hunt (in rugged terrain), can use a self-climbing tree stand, take the grandkids fishing and sleigh riding (and I participate). Every year my Flexible Flyer (that I have had since I was 5) sees the snow again! I also go for hikes or bike rides with the wife and / or kids/grandkids.
Like the Adirondak Mountain Man Rondeau said: "Father time keeps picking my pocket, and I can't seem to get him to stop".
I try hard to do a routine that stops me from declining most years. My advice, just do the best you can, but work on it! Stay active for as long as you can.