The development or at least the development potential is characteristic of the whole life of man. Although some theorists claim that the "adulthood" is divided into a number of well-known stages of development, the development process itself in maturity differs from the developmental processes in childhood and adolescence. Changes in adult thinking, behavior, and personality are negligible in chronological age or in specific body changes.

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 To a much greater extent, they are determined by personal, social and cultural events and factors. Social orientations or cultural conditions of a young adult can support, widen or worsen forms of behavior in the teen years and require the development of new ones. Young people find themselves in need of choosing and solving many problems. The ability to respond to changes and to successfully adapt to new conditions is usually considered as a maturity criterion. In adults, we no longer have physical targets like, for example, puberty, or with well-defined stages of cognitive development that will show us when a stage of development ends and another begins. 

Instead, in the course of adult development, it is marked by certain social orientations, as well as by the roles and relationships involved in the composition of family life and careers. Adult development depends on roles and relationships in living life, on physical changes, on acquired knowledge, habits, skills and experience, on life crises and on the loss of the state of peace or war. When it comes to adult psychology, three sub-periods or three stages are considered: youth / early maturity / from 20 to 40 years; maturity (from 40 to 60 years); old age (after 60 years). Each of these large phases of adulthood is characterized by a variety of psychological problems. Freud and Eriksson think that a person becomes a mature person when he takes responsibility for his love and work. And we will really see that many of the important issues of adulthood revolve around these two critical themes.

 Of course, even these age-based guidelines do not always fit exactly with the perception of the behavior in question in the course of life. According to different authors these limits are different. Since it is difficult or impossible to define the stages of development of elderly people by age alone, researchers have come to the notion of "age clock". It means a type of internal time schedule of life used as a criterion for adult development.