The idea that I originally thought I would use for the Jupiter Challenge — that of the girl finding her origins in the mirror world — dates from 1997, when I was 19. Thus it’s three years too recent for consideration, as story ideas used in the challenge must have been generated at age 16 or before.
In other news, I have unearthed my trove of story outlines and discovered some alternative ideas that I did indeed think up before 16.
There’s the one where the girl writes a creation myth and makes a world, which she then enters, where she is worshipped as a god. She has to defeat her personified fear of death, which is causing people to sicken and die.
There’s the one where the boy has a magic ring inhabited by the soul of his dead aunt. He and she join forces to defeat someone who yanks them from Earth into a magical world because she wants the ring.
There’s the one about the princess who’s white as snow, red and blood and black as ebony, but never at the same time, more like a series of three different appearances and corresponding personalities, and her search through a bunch of fairy tale tropes to find a cure for her condition.
There’s also a bunch of deliberately pointless quest narratives in which the sought-for object is never fully elucidated or centralized as much as the relationships between the people on the quest.