“Teenager” is a word I had to avoid in my novel set in 1924. The first known use of the word in print did not come until 1941 in–of all places–an issue of Popular Science magazine. But this all-American word has British parents.
The word “teens” has been documented as far back as 1673. Phrases like, “A young girl in the teens” or “Her daughter who was by this time come into the Teens,” appear in the late 1600s and early 1700s, but not the word “teenager.” Note that “teen” is NOT a shortened version of “teenager,” since “teen” came first by over 250 years.
And “teen age” was first used as an adjective in 1921, as in “all teen age girls of the city are cordially invited to attend . . .” But not “teenagers,” who weren’t invented until the 1940s during World War II.