Realistic goal yes but my point was and is as you get older it will be tougher. Plus increased age = increased miles hence double whammy.
This is an interesting discussion. I tend to agree with your general point but feel there is a lot one can do to mitigate or perhaps manage this.
At 72 I can still ride on rolling/flat at the same level as at 67/68 and definitely at the level I was two years ago. Where my ability has declined is in climbing. When I say climbing I mean 3½/4 miles or more ascent, not a short, sharp ascent. Broadly I've lost a minute a year, some climbs are four minutes longer, others six. I need to add some context to the climbing point. Late June 2024 I had a major RTC and lost 9/10 months of real riding. Six years ago, 2020, is the point where I make my comparison, lockdown and nothing to do except ride two hours a day, I was at a peak. It's impossible to calculate the impact of these events.
I'm working at the gym to manage any decline in three ways:
general stretching
pelvic and core stability
cycle specific strength training
As a result of the above my muscle mass is increasing as is my bone density. Both unusual in older people.
Aside from investing in myself I've bought a new bike, more lightweight and aero, a bike built for endurance. I equipped it with GRX to help with both climbing and endurance. Last week I was on a route I last rode in early June 2024. 73 miles and 6000 feet. The GRX was a dream, the climbing was noticeably easier.
I think your overall point is correct. I have several friends who say the same but we are all working to manage this. What is difficult, perhaps impossible?, is improvement.
I find recovery times are longer. The days of regular 200 mile weeks, say 3 x 70, have been replaced with 130 - 150 mile weeks and extra rest days. It all helps to add to longevity.
My expectation is to ride 90 miles at 90 but it may well be a couple of hours longer and the only ride of the week. 🤣