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).
Student or Learner