At eight, new teeth grow.
At sixteen, he is full of vital essence.
At twenty-four, the kidney qi is full.
At thirty-two, his muscles and bones are strong.
At forty, he begins to lose hair.
At forty-eight, his face is withered.
At fifty-six, his vital essence is deteriorated.
At sixty-four, he begins to lose his teeth.
Learn more about the theory of Chinese medicine, please read Physiological Functions of Kidney