Lotta variables beyond aging. How you handled the heat/humidity from a drinking/eating/rest perspective is one. I'm 64 - the hardest ride I've ever done was a flat century ride when I was about 35. It was on a killer hot day on Maryland's eastern shore, into a headwind for the last 40 miles, in the peak of the heat. Back then I didn't pay much attention to drinking (now known as hydration...) and I'm sure I was dehydrated. At age 62 I did a very similar century ride in similar conditions but I'm smarter now! Forced myself to drink more and eat more than I wanted to. Felt better and pretty much matched my time from 25+ years ago.
This year, I've seen the "high mileage but mostly short rides" effect of staying safe during the pandemic. I have an indoor trainer, so I've been able to mix in hour long interval rides to get more training gain than I can on 25 mile rides out on the road. That really seemed to help on my only 2 long rides this year, a flat (cool but crazy winds) century and an 82 mile rolling hills ride. But I did still get in a few 50 and 60 mile rides in advance of those - I find that my butt needs that before long rides!