Logic would suggest that “ability to cycle a decent distance, provided you keep reasonably in practice” curves would look the same, displaced to the left by maybe ten or fifteen years.
I’m a mere 65yo, and (touch wood) although I definitely need to pace myself, and need lower gears on hills than I used to, I don’t feel any step change, so far. But, I’ve never been an athlete, only ever a bloke who thoroughly enjoys bike rides, so I’ve probably never pushed myself in the way that some here clearly have.
I’ve met people well into their eighties who I can barely keep up with, and get overtaken going up hill by people in their mid-seventies, so a few people do sustain seriously well. Those I know who have given up it’s either a very specific health issue (my mother gave up at 82 because she had trouble maintaining balance, for instance), or road cyclists who have simply got sick of feeling terrified by cars and Lorries. My grandfather took a different approach: he was a daily utility cyclist, only transport a bike, and rode decent distances carrying his tools (a gardener), or his golf clubs; he put his bike in the shed when he got home one evening, aged 85, and never woke up in the morning.
Just think though: a very high % of the population, even youngsters, don’t have the fitness or stamina to ride a decent distance at all, because they don’t keep in practice.
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