Biological systems seeks homeostasis on a very deep level. A lot of our brain is devoted to normalizing volume and brightness, for example.

The reason chili enthusiasts need more over time is basically the same as the reason heroin enthusiasts do.

But our sensitivity to temperature doesn't decrease with age, if anything the opposite... even if that's more obvious with ambient rather than tactile temperature (which I'd imagine are processed quite differently by our nervous systems).

Taste sensitivity declines with age. Strong flavours like smelly cheese are disgusting for kids but enjoyed by older adults.

They are enjoyed by adults who acquired that taste: https://en.m.wikipedia.org/wiki/Acquired_taste

For instance, it would be really hard to find anyone, no matter how old, who enjoys surströmming or hákarl without having become acquitted with them.

Acquainted :) Though perhaps they are used as part of the Swedish justice system?

I always thought that the endorphin high is unrelated to the beneficial effect: any strong pain is normally followed by a release of endorphins to compensate. It's why pain and pleasure are often difficult to disentangle. A strong dose of capsaicin will induce a painful sensation in the mouth (you'll feel like burning), which is compensated by a release of endorphins.

The desensitization to hot peppers happens at a much smaller scale than years, so it doesn’t have much to do with your age.