Etymology
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age (v.)
late 14c., "grow old," from age (n.). Transitive meaning "make old" is early 15c.
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age (n.)

late 13c., "long but indefinite period in human history," from Old French aage, eage (12c., Modern French âge) "age; life, lifetime, lifespan; maturity," earlier edage (11c.), from Vulgar Latin *aetaticum (source also of Spanish edad, Italian eta, Portuguese idade "age"), extended form of Latin aetatem (nominative aetas), "period of life, age, lifetime, years," from aevum "lifetime, eternity, age," from PIE root *aiw- "vital force, life; long life, eternity"

Expelled native eld (Old English eald) "old age; an age; age as a period of life." Meaning "time something has lived, particular length or stage of life" is from early 14c. Used especially for "old age" since early 14c.; meaning "effects of old age" (feebleness, senility, etc.) is from mid-15c. In geology, in reference to great periods in the history of the earth, 1855; in archaeology, from 1865 (Stone Age, etc.) naming periods for the materials employed for weapons and tools. Sometimes in early modern English "a century" (similar to French siècle "century," literally "an age"), hence plural use in Dark Ages, Middle Ages. To act (one's) age "behave with appropriate maturity" is attested by 1927.

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age-group (n.)
1876, originally a term in the science of demographics, from age (n.) + group (n.).
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New Age (adj.)
1971, in reference to a modern spiritual movement, from new + age (n.). It had been used at various times at least since the 1840s.
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over-age (adj.)

that is over a certain age," "1886, from over- + age (n.). Related: Over-aged (n.) "those who are too old" (late 15c.).

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middle age (n.)

"period between youth and old age," formerly generally understood as 40 to 50, late 14c., from middle (adj.) + age (n.). The adjective middle-aged "having lived to the middle of the ordinary human lifespan, neither old nor young" is by c. 1600.

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ice age (n.)
1855, from ice (n.) + age (n.). Perhaps translating German Eiszeit (1837). An earlier term in the same sense was glacial epoch (1841). Local scientific men had noticed from the late 18c. evidence that the Alpine glaciers once had been much larger; in the 1830s stray boulders, moraines, and polished bedrock in northern Europe (formerly interpreted as relics of catastrophic floods) began to be understood as revealing the former presence of a large ice cap there. When Agassiz, a convert to the theory, came to America in 1846 he found similar evidence in New England. The glacial theory and the notion that there had been several worldwide ice ages seems to have been generally accepted by the 1870s.
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-age 
word-forming element in nouns of act, process, function, condition, from Old French and French -age, from Late Latin -aticum "belonging to, related to," originally neuter adjectival suffix, from PIE *-at- (source of Latin -atus, past participle suffix of verbs of the first conjugation) + *-(i)ko-, secondary suffix forming adjectives (see -ic).
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