Uh oh, did the Teenage Mutant Ninja Turtles get it wrong? Some stuffy grammarians might just raise their noses, insisting these were “teenaged” mutant ninja turtles. In fact, that was the first form of the word and therefore correct, they’d say. But don’t listen. They’re wrong.
I don’t know what it is about this word in particular, but for some reason certain people insist that “teenaged” came first. My guess is that they’re making a connection to words like “ice(d) tea,” “skim(med) milk,” or “whip(ped) cream,” where the final “d” has been lost over time. However, the first use of “teen-age” was in 1921. “Teen-aged” didn’t appear until the early 1950s. Of course, the hyphen was lost over time too.
So what does this all mean when it comes to what form is correct? In American English, “teenage” is the most common and most accepted form. So don’t call out those ninja turtles – not that you’d want to anyway. They’d probably win the fight.