Teenage

google

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early 20th century (originally in the US): from teen + age.

wiktionary

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From teen ( Kentish variant of tine(“enclose within a wattle fence”)) +‎ -age(“ suffix forming abstract nouns”). First attested circa 1700.

From -teen +‎ age. First attested in 1921.

etymonline

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teenage (adj.)

also teen age, teen-age; 1911, from teen + age (n.). Originally in reference to Sunday School classes. Teen-aged (adj.) is from 1922.