In addition this is time when fertility for both sexes is achieved and important psychological changes occur. It occurs on average at 12 years in girls and at 14 years in boys. Pubic hair appearance starts shortly after breast growth begins. By this time, the vagina has already begun to lengthen and the uterus is slowly enlarging. On the onset of menstruation, breast growth nears completion and almost invariably comes after the peak growth spurt.
Menstruation is influenced by socio economic factors, climate, heredity, family size and nutrition.
The age at menarche varies from 8-16 years. Physical changes due to puberty start occurring by the age of 14 years. Earliest change is the growth of the testes. Then growth of the penis. Genital development occurs from 11-15 years.