“The Yellow Emperor’s Canon” says:
Women are at the age of:
7: Kidney Qi begins to flourish; Baby teeth start to lose; Hairs start to get thicker.
14: The vitality begins to flourish; Menstrual starts; Puberty begins.
21: Kidney Qi is strong; Adult teeth fully grow.
28: Muscles & bones are strong; Hair grows vigorously; the body is very strong.
35: Qi/Blood is weakening; Face begins to languish; Hair starts to lose.
42: Qi/blood is weak; Face gets haggard; Hair begins to turn grey.
49: The meridians, Qi/Blood are weak; menopause and aging.
Men are at the age of:
8: kidney Qi begins to flourish; Baby teeth start to lose; Hairs start to get thicker.
16: Qi begins to flourish; Puberty begins.
24: Bones are stronger and stronger; Adult teeth fully grow.
32: Bones are very strong; Muscles are full of strength.
40: Kidney Qi starts to decline; Hair begins to shed; Teeth begin to age.
48: The upper Yang Qi gradually fades; Face gets haggard; hair & temples turn grey.
56: Qi/blood is weak; Tendon activities were not flexible.
64: Less energy and physical fatigue; loses teeth and hair; kidney gets weaker; fertility ends.