1670s (plural), "teen-age years of a person," formed from -teen taken as a separate word. As "decade of years comprising numbers ending in -teen," from 1889.
"teen-aged person," 1818 (but rare before 20c.), from -teen. As an adjective meaning "of or for teen-agers," from 1947.
A teenage person; teenager: a really interesting biz for a teen who loves being busy/ a robust health that would be remarkable on a teener/ ''You only pass this way once,'' he tells a teenie in persuading her to come along for a ride