How long would I last at 50c / 122F?

When we have long periods of hot weather, more old people die. Why? Do I have better temperature regulation than old people? Would I die after “n” days of 120F and nights of 90F, even if I kept out of the sun and had water and a fan?

What sets the limit for human survival?

(Triggered by reading that domestic cats are desert animals and can handle 55C, 130F conditions)

That’s still in the “It sucks but people live in it” range. It hit 127 when I was in Kuwait. I couldn’t wait to get out of there but people live there without bursting into flames.

I’m sure that smarter people than I will be along shortly but I’d wager that you can live nearly indefinitely at such temps with shade, minimal exertion, ample water and nutrition (including electrolyte support). A low humidity environment would greatly help though.

Obviously old people are more susceptible to any extreme conditions, or to disease, because they are simply less robust. I’m not sure what the question there is.

When ambient temperature exceeds body temperature, the only way to dump excess heat is by evaporative cooling, so it’s critical to have continuous replacement of the water and electrolytes lost through sweating. Above 100F without a water supply you will die quite quickly. And this is why ambient humidity is so critical - much easier to survive in low humidity when your sweat will evaporate quickly. At low humidity, you can’t really put a specific hard ceiling on what temperature we can withstand, it just becomes progressively more and more difficult to dump enough heat as the temperature rises. At 100% humidity, ambient temperature equal to body temperature is a hard limit, because sweat won’t evaporate. Other things being equal, people with a large surface area to mass ratio will cool better - so better to be tall and thin.

During a bad heat wave in Chicago some years ago, many elderly people died. But they stayed cooped up in their apartments with the windows closed as they were afraid of break-ins. The ones who survived went to some air-conditioned place during the day even if they were in a walk-up.

The perception of temperature in the elderly is definitely different. My grandmother lived in an old house with no circulation. She did have a wall-mounted air-conditioner. She would never turn it on the matter how hot it got. She had a tiny window fan in one small window on the second floor. She tried to convince us that it cooled down the entire house. Whenever it got really hot my mother had to go over there and make sure the air conditioner was on for at least some of the time. She did live to be 104 so she was doing something right.

The highest temperature that you can be exposed for prolonged times and survive is a wet-bulb temperature of 35 deg Celsius.
(see https://en.m.wikipedia.org/wiki/Wet-bulb_temperature for an explanation of wet-bulb temperature). At 50 deg Celsius, a wet bulb temperature of 35 deg is reached at approx 40% r.H. Above that, even when in the shade and next to a fan, you will eventually overheat.

Yes.