1921, formed from -
teen as a separate word +
age; derived noun
teenager is from 1941 (the earlier word for this was
teener, attested in Anmer.Eng. from 1894).
Teen-aged (adj.) is from 1952; shortened form
teen is from 1951 (though this had been used as a noun to mean "teen-aged person" in 1818).
Teeny-bopper is recorded from 1966, from
teen but also felt as infl. by
teeny. For second element, see
bop.