In my 30s I loved riding on hot days. I would sweat like crazy which had a nice cooling effect - except for sweat in the eyes.
In my sunset 60s, the heat is no longer my friend. I cannot put out the same amount of effort (this is compared to cool days - not aging) and just don’t feel as snappy. Last year it was 95 and I was doing a quick 30 miles. This ride was after doing several acclimation rides, where my Garmin dutifully kept telling me how acclimated I should be. I stopped in the sun to take a picture and All of a sudden I had a tremendous feeling of vertigo and had to sit down as everything was spinning. Drank the last 1/2 a bottle of water and sat for about 10 minutes until the vertigo was pretty much resolved. I was a bit nervous getting back on the bike for last two miles, but made it fine. When home, I drank lots of water and some electrolytes.
In the future I will drink far more, not push for PRs, and take shady breaks.