This is an enlightening thread. I'm drawn to it like a 56 year old moth.
At the risk of a tangent, at what age do we "50+ers" feel we still can go on some epic ride/adventure? As running became jogging I turned to biking in my 40s. When I turned 50 I joined a gaggle of 5 fellow geezers for occasional weekend rides and a once a year, one week bike trip. I averaged <2000 mpy.
This year I stepped biking up to 4700 miles and lost a bunch of weight. Why?
Mid 50s earning power and weight reached new highs and fitness new low; I felt I'd better do something now if I wanted to experience another great physical adventure (biked across the US, ran marathons, etc. in my youth). I flatter myself thinking I am average in the main herd; I'm certainly not one of those 75 year old hotshots climbing Kilimanjaro or running Boston at 85. I'm already old enough and apparently not smart enough to manage my exercise regime without injuries.
Does it make a difference if I execute a rationally designed, age appropriate workout plan or dream of one more epic ride, dream of winning a race or showing up a much younger rider. For me I choose gathering geezers, dress up in spandex and push as I lead my fantasy break-away.