70 yo here. I have far less ability to generate heat for hours by keeping my speed and power output up. Late in rides, sun getting low, I used to just power to the barn. Doesn't happen now. And if I don't have the clothes to put on, I cool and slow further. (To the point where it can get scary or sickness prone.)
Aging - two ways of thinking about it. It sucks. It could be better than the alternative.