The social changes of the last few decades have resulted in the revaluation of the classic life-stage models. The time of finding active employment and establishing a family have been postponed, thus not supporting self reliance and undertaking adult roles. In our comprehensive study we discuss the social and demographic phenomena that have contributed to the formation of post-adolescence. We analyse the significance of optional life-patterns which appeared instead of the standard life-course, as well as the change in the criteria system of adulthood and the separation dimensions. We review the psychoanalytic and psychosocial theories of adolescence- the theory of the Erikson adolescent crisis and Marcia's psychosocial moratorium theory, together with the cognitive patterns that lie in the background of post-adolescence, and the changes in lifestyle that characterize the social adaptation of youngsters. The differences between the Peter Pan syndrome and prolonged adolescence crisis are examined in the aspect of transaction-analysis. We take account of the psychic disorders, due to which these people seek for psychiatric help.