Interesting post…I’m not sure I can add anything new beyond the great insights that have already been shared other than to be another example of one who is currently sitting at 4.1 watts/kg at age 56. I have been riding and competing for about 10 years but only started using a Power Meter and following a more structured plan, through TrainerRoad, over the past year. My 1st FTP test showed a result of 294 Watts while the most recent FTP test last week showed progress to 318.
It can be done! (Full disclosure: although I had been a collegiate wrestler in the early 80’s at a Big 10 University, I do not think much of that prior fitness from 35+ years ago had much to do with my current cycling fitness results. Perhaps it is more mental and be willing to endure pain; that is one thing the two sports have in common!