Why are European and American men generally older than Asian men?

Sperm is very sensitive to temperature. If the temperature is too low, its activity will be poor, resulting in a low pregnancy rate. If the temperature is too high (about 40℃), it will be killed or inactivated.

In the sub-cold zone and tropical race, the sex organs must go deep into the body to ensure proper temperature.

Temperate zone requirements are not so high.