The term adolescence was invented to describe this in-between period in which young people are neither children nor adults. Adolescence begins with a period of physical development marked by a growth spurt that leads to puberty the maturation of the primary sex organs. The timing of this process can vary a great deal among individuals of both sexes. For girls, the onset of puberty occurs between the ages of nine and fourteen, with twelve being the average. A year or two later there is a sudden increase in height and menstruation begins.
Boys start to mature physically around the age of eleven.
The first sign is the enlargement of the testicles, followed by the appearance of pubic hair, changes in the penis and broadening of the shoulders. A boy's growth spurt usually occurs around age fourteen when the voice deepens and facial hair begins to appear. In any culture, teens have a natural need to establish their own identity. Adolescents must progress from childhood dependency to adult independence from being subject to the authority and control of parents to exercising personal autonomy and self control. Separating from parents and establishing one's individuality is a normal and necessary step in personal development.