I was surprised by how many examples I found in newspapers of
tween, in the sense of a person just younger than their teens. In the paper you mentioned, MK, the
Guardian,
tween appears much more often than the longer form
tweenager. A recent example, from 8 May:
Also firmly in the counter-programming zone is tween dance flick All Stars, a junior spin on the street-dance movie phenomenon.
Many of the articles using the word are about entertainment or fashion. Perhaps (like me) you don't read those sections of the paper much, MK. And it may be that the word is used more frequently in the media than in conversation, being basically a marketing concept.
I found a few examples of
tween in fiction. Oddly, many of these examples were from science fiction. There is an old gag that says the Golden Age of Science Fiction is twelve, so perhaps SF authors are writing about tweens because they suspect that is the age group most likely to read their work.
My conclusion is that this word does not quite have the breadth of usage that would justify it remaining common, so I'll switch it to rare.
