Middle age is the period of life roughly between ages 40 and 65, when people are no longer young adults but not yet elderly. During middle age, people often have well-established careers, may be raising teenagers or college-age children, and start noticing physical changes like needing reading glasses or finding gray hairs.

The term comes from the idea that these years fall in the middle of a typical human lifespan. Someone in middle age has accumulated significant life experience and often holds positions of responsibility: they might manage teams at work, serve on school boards, or run businesses. Many of history's greatest achievements came from people in middle age who combined youthful energy with hard-earned wisdom.

Middle age brings interesting contradictions. A middle-aged person might feel simultaneously experienced and uncertain, energetic yet aware of physical limits, established yet still pursuing new goals. People in middle age may find themselves caring for both their children and their aging parents, which some call the “sandwich generation.”

The phrase middle-aged can be used as an adjective, as in “a middle-aged professor” or “middle-aged responsibilities.” When someone jokes about having a midlife crisis, they're talking about the anxiety some people feel during middle age when they wonder if they've accomplished what they hoped to.