The term teenager didn’t start making its way into popular usage until the 1930s and 1940s. The first instance of the word that I found in an Idaho paper was in the Statesman in 1941. It didn’t come up again there until 1943.
Teenage came along a little earlier, though newspapers were slow to standardize it. They used teen age, ‘teen age, “teen” age, and teen-age, depending on the whim of typesetters, perhaps. An expert on the teen-age from Chicago was speaking at a Boise church convention on “the boy problem” in 1914. Thank goodness we’ve now solved that one.
This wasn’t just about semantics. In a sense, there were no teenagers throughout most of recorded history. There were children who toddled around until they were five or six or seven, not contributing much to a family. Once they could start working at some menial labor, that’s what they did, simply becoming more useful as they got older.
The introduction of standardized education and child labor laws began to change this in the 19th century. Some scholars attribute the invention of the teenager, more or less as we know them today, to the automobile. Cars provided freedom for young people to occasionally get away from their parents. Dating became much more common. Then consolidated high schools began to use buses to bring students from further and further away. There they were, together, learning, dating, and beginning to dress in their own fashions in the 1950s (picture). Voila! Teenagers!
I have done no research on the subject, but feel confident that eye-rolling and insolence came into vogue about the same time as the word teenager.