It takes 21 years to grow a human adult.
Adolescents have large secretions of hormones.
For boys the hormone is testosterone, and for girls it is estrogen and progesterone. Testosterone causes the male drive which is associated with the urge to compete, to seek a mate, and to fight. It is abnormal for a male to do otherwise. For centuries this natural tendency has been directed into early marriage, rearing a family which takes tremendous energy, and participating in community life. The urge was harnessed via exhaustion.