Muscular strength, reaction time, sensory abilities, and cardiac output begin to decline in the late twenties and continue to decline through middle adulthood (to age 65) and late adulthood (after 65).Around age 50, menopause ends women's period of fertility. Men do not undergo a similar sharp drop in hormone levels or fertility.In late adulthood, the immune system also weakens, but good health habits help to enable better health in later life.