It's like exercising; if you don't use it you lose it and once you're too old, you can't get it back. But, if you keep it up you can carry it into an ancient age. I knew very old people who could still touch their toes, lift heavy loads, and lay out in the absolutely baking sun.
I'm well past middle age and so far I can still do strenuous exercise outside at 103. I can physically feel that it is hot, but things still work. Use it or lose it. If you are under 40, I'd really suggest working out your heat-coping body systems, double so if you're under 30.
Read up on heat stroke, listen to your body and treat your body as intently as if you are lifting heavy weights. You can hurt yourself under both conditions, but if you listen and you build and you strengthen, you can have a body that is a treat to live in.


