I am in my 60's. I used to time trial many years ago, and have been riding bike most of my life since my pre teen years. I have had a few gaps, the longest between 50 and 61 years old. Then I started again to try and shift weight. It hasn't worked, I was 18 stone 6 months ago and I am still 18 stone despite doing over a thousand miles. Truth is I eat too much!
However, I have found that my climbing ability has never been so good. When I drive a route that I also ride some of the hills frighten me, yet I am just going up them with little trouble. Bear in mind this is Essex though, not the Pennines, thank heavens. We might have a different definition of hills.
I agree with what has been said about recovery time. If I do a thirty miler in my average of 2.5 hours (I didn't claim to be fast!!), there is no way I could do it agin the next day as I could twenty odd years ago. For longer rides I have to do alternate days, then I often go for a walk on the off days.
Much of the time I just go out and ride and take pleasure in being out with no pressure to perform. Any pressure is self induced, except when being overtaken by a gorgeous 20 something young lady in very tight tights and I try and keep up for a few yards. That is when age and performance do (and would) fail me.........