A baby goes through various stages f growth after it is born. The most obvious changes are the progressive increase in height and weight until the child becomes an adult. There are other more complex changes, all of which will not be discussed here. Growth after birth can be divided into three stages- infancy, childhood and adolescence.

Infancy, the first two years of a baby’s life, is phase of very rapid growth. This is when a baby learns to sit, stand, walk and speak. The next 10 years, called childhood, are marked by steady physical and mental growth.

Adolescence

The second phase of rapid growth occurs between 10 and 18 years. In this phase, called adolescence, an individual becomes sexually mature, or capable of reproducing. The age of attaining puberty, or sexual maturity, varies from person to person, but generally, it is between 11 and 13 years in the case of girls and around 13 -14 in the case of bays.

In girls, puberty is marked by the onset of menstruation and external physical changes like the enlargement of breasts, growth of hair in the pubic region and armpits, and the widening of the pelvic girdle. These changes take place under the influence of Progeststerone and Oestrogen, two hormones secreted by the ovaries. The uterus also grows in size during this phase.

In boys, the corresponding changes are the growth of hair in the pubic region, the armpits and the face, and the deepening of the voice due to the enlargement of the larynx. The penis and scrotum enlarge and sperms are produced by the tests. These changes are influenced by a hormone called testosterone, secreted by the tests.

The visible or external changes that occur in boys and girls at puberty are called secondary sexual characters. Adolescence, however, is not only about attaining sexual maturity, increase in eight and weight and the development of secondary sexual characters. It is also about tremendous growth emotionally and intellectually. Some of the emotional changes occur due to chemical changes in the body. These are together with the pressures of `growing up’ or becoming more socially responsible and independent often create emotional turbulence in growing adolescents. They may feel insecure, anger, rebellious, sad, boisterously happy, restless, and so on. Intellectually, a growing adolescent becomes more and more capable of analyzing, reasoning, putting things together and drawing conclusions.

Adulthood

As an adolescent grows into a young adult, he or she continues to grow mentally and emotionally. A part of this growth consists of learning to be independent, forming relationship and starting a new family.

There is no fixed age at which one can say that the mental and physical abilities of an adult start declining. In most societies, people retire from work at around 65. They start slowing down, as old age sets in, but the process of slowing down varies from person to person.