Life course: socially constructed stages that people pass through as they live out their lives. Early teens cannot do legally what later teens can. Poor teens less likely to have a job or be in school. Young people are staying at home much longer delaying the next stage. Traditionally the time to get established, but now is more difficult, if not postponed. Income and prestige are at the peak, but signs of physical aging begin. Older people are an increasing percentage of the population. Gerontology: a branch of social sciences dealing with aging and the elderly. Growing old involves biological changes; how a culture defines this stage of life makes a difference in the reality of old age. Researchers report three levels of old younger old older old oldest old. Seniors are a socially diverse population in terms of economics, race, ethnicity, and gender. Aging places stress on the individual and society.