Many well-established developmental theories concentrate on strategies of regulation and try to explain how individuals compensate for possible losses in old age. In public debates, and in laypeople's perception of aging, however, activity and productivity seem to be central concepts associated with successful aging. The present research focuses on subjective developmental theories on aging from an older individuals' point of view. Within this research project, the aim was not only to focus on older individuals' perceptions, but also whether they are similar or potentially different to younger adults' views on aging, since younger individuals are more distant to a concrete idea of what it means to 'be old'. In a first qualitative study interviews with older individuals were conducted, focusing differences in subjective theories on aging. In a second study two sub-samples of adults (225 older adults, aged 60 to 100 years and 194 young adults, aged 18-30 years) were investigated concerning particular aspects of successful aging, including activity and disengagement. Both studies give evidence for the importance of balancing gains and losses and show the relevance of both, activity and disengagement for successful aging. Moreover, the importance of control over individually meaningful aspects for successful aging is discussed.