Old age consists of ages nearing or surpassing the average life span of human beings, and thus the end of the human life cycle. Euphemisms and terms for older people include seniors — chiefly an American usage — or elderly. As occurs with almost any definable group of humanity, some people will hold a prejudice against others; in this case, against older people. This is one form of ageism.

Older people have limited regenerative abilities and are more prone to disease, syndromes, and sickness than other adults. For the biology of ageing, see Senescence. The medical study of the aging process is gerontology, and the study of diseases that afflict the elderly is geriatrics.