Middle adulthood refers to the stage of life where a person is in their forties to sixties. It is the period between early adulthood and old age. Full definition
In that case, the skin cells became striatal medium spiny neurons, which are affected in Huntington's disease — an inherited, eventually fatal genetic disorder that causes involuntary muscle movements and cognitive decline beginning in middle adulthood. (sciencedaily.com)
Personality disorders evident by early adulthood and risk for anxiety disorders during middle adulthood (cambridge.org)
Stages: Infancy Childhood Adolescence Adulthood - Early adulthood Middle adulthood Late adulthood (psychology.wikia.com)