The latter part of life, the part of life after one's prime.

(archaeology) A period in a civilization's development when the most advanced metalworking has developed the techniques of smelting copper from natural outcroppings and alloys it to cast bronze.

A demographic grouping based on age.

(sciences) A period of long-term reduction in the temperature of Earth's surface and atmosphere, resulting in the presence of major polar ice sheets that reach the ocean and calve icebergs.

Used other than figuratively or idiomatically: The least age at which one is permitted by law to drink alcoholic beverages. / (poker slang) A two and an ace as a starting hand in Texas hold 'em

plural of age of majority

(see usage notes) The period of European history encompassing (roughly) 476–1000 CE. / (Ancient Greece) The Greek Dark Ages (c. 1100–750 BCE). / The dark ages of Cambodia (c. 1450–1863).

plural of age group

(history) The period of primarily European history between the decline of the Western Roman Empire (antiquity) and the early modern period or the Renaissance; the time between c. 500 and 1500.

Synonym of prehistory: the era before written records.