In biology, the physiological life span of mammals is standard. Some professionals have found through research that the length of physiological life should be 5-7 times that of growth period. The growth period of human is calculated according to the growth time of teeth. People are between the ages of 20 and 25, and most of the last teeth have already grown, so it is estimated that the physiological life span of people should be between 100- 175 years old, which means that the longest life span can reach 175 years old.