Old age is the range of ages nearing and surpassing the life expectancy of human beings; it is the end of the human life cycle. Terms, some of them euphemisms, for people at this age include old people, the elderly (worldwide usage), OAPs (British for Old Age Pensioner), seniors, senior citizens (American), older adults (in the social sciences), and elders (many cultures). Old people often have limited regenerative abilities and are more susceptible to disease, syndromes, injuries, and other illnesses than younger adults. Some disciplines and domains focus on the aging and the aged, such as the organic processes of aging (senescence), medical studies of the aging process (gerontology), diseases that afflict older adults (geriatrics), technology to support the aging society (gerontechnology), and leisure and sport activities adapted to older people (such as senior sport). The elderly face social problems related to retirement, loneliness, and ageism. Old age is not a definite biological stage: the chronological age denoted as "old age" varies culturally and historically. In 2011, the United Nations proposed a human-rights convention to protect old people.
