| Noun | 1. | middle age - the time of life between youth and old age (e.g., between 40 and 60 years of age)time of life - a period of time during which a person is normally in a particular life state adulthood, maturity - the period of time in your life after your physical growth has stopped and you are fully developed climacteric - a period in a man's life corresponding to menopause | |