In the 80/90 timeframe, a very talented lady would do her long rides with our local Wheelman club. She did a lot of miles. I raced for a small local bike shop team. She was on the top local team and she won many national championships over the years and still does. I seem to recall her being a 56 minute 40km TTer back in the day and that would always win. Many decades later, she recently did 34 minutes for 20 Km and still won the national championship. She has won a bunch of them. So, she got slower but not slow.
I was recovering in a small cafe a few years ago and in walks a rider with a Stars and Stripes jersey (National Champ jersey) and I did not think she would remember me after all those years. She was suffering like I was with coughing, so, I strike up a conversation. We got into challenges as one ages but the dirty air was the main topic. I had just been diagnosed with asthma. She told me similar age breathing woes. Interestingly she said she "rides like crap" until the air clears out in early Summer and she was giving me encouragement to give it time. She was right, I now notice that my power is lousy when my breathing is labored and albuterol inhaler helps a little but not totally. If someone rolls coal on me, I instinctively reach for my inhaler. She wasn't sure she could make it the 10 miles back home but she had learned to deal with it. About 2 months later she won the TT. Yet, on that day she was looking pretty bad. She was sure it would pass. It is these types of challenges that make it interesting. I have arthritis in my left hip and it can make riding hard. Dealing with injuries and various medical issues is probably a bigger challenge than I expected as I get old. So, I think staying healthy to be able to keep a consistent level of training is a key factor for me as I get older.
The TT times and records by age are pretty revealing. USA Cycling lists them