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"period between youth and old age," late 14c.; middle-aged (adj.) first recorded c.1600.
middle age mid·dle age (mĭd'l)
The time of human life between youth and old age, usually reckoned as the years between 40 and 60. Also called midlife.
period of human adulthood that immediately precedes the onset of old age. Though the age period that defines middle age is somewhat arbitrary, differing greatly from person to person, it is generally defined as being between the ages of 40 and 60. The physiological and psychological changes experienced by a middle-aged person centre on the gradual decline of physical abilities and the awareness of mortality. In middle age, the relative potencies of past, present, and future are altered as the individual increasingly directs effort to the process of reminiscence and recollection of the past, rather than anticipation of the future. If approached constructively, middle age can prepare an individual for a satisfying and productive old age. See also psychological development.