adulthood
n. the period of human development in which full physical growth and maturity have been achieved and certain biological, cognitive, social, personality, and other changes associated with the aging process occur. Beginning after adolescence, adulthood is sometimes divided into young adulthood (roughly 20 to 35 years of age); middle adulthood (about 36 to 64 years); and later adulthood (age 65 and beyond). The last is sometimes subdivided into young-old (65 to 74), old-old (75 to 84), and oldest old (85 and beyond). The oldest old group is the fastest growing segment of the population in many developed countries. See also emerging adulthood.