In Japanese news, I’ve heard that elders are more vulnerable to it because they are not as sensitive to the harmful levels of heat, so it feels fine but they end up with heat stroke due to not putting on air conditioners or fans and getting enough water.

A source for claim in Japanese

1. An older person’s body has a lower percentage of water
2. Less sensitive to heat and thirst
3. Ability to sweat and dispel heat is lower