I'm not sure what you're asking. But one possibility comes to mind; it is based on the idiom 'n [years old] coming on n + 1'. For example a child who is '10 going on 11' will have their 11th birthday soon. I think there was a song in The Sound of Music with the title "I am 16 going on 17" - that is, I know there's a song, but I'm not sure of the show.
A girl who is in a hurry to be seen as a grown woman is sometimes said to be, say. '6 going on 16'. (I first heard this about 30 years ago, but I've heard variations quite often since then).
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