Old age comprises "the later part of life; the period of life after youth and middle age . . . , usually with reference to deterioration". At what age old age begins cannot be universally defined because it differs according to the context. The United Nations has agreed that 65+ years may be usually denoted as old age and this is the first attempt at an international definition of old age. However, for its study of old age in Africa, the World Health Organization (WHO) set 55 as the beginning of old age. At the same time, the WHO recognized that the developing world often defines old age, not by years, but by new roles, loss of previous roles, or inability to make active contributions to society.