I started writing fanfiction in Jr. High. STtOS was still on the air in its first run. Voyage to the Bottom of the Sea was in reruns after school, right after Dark Shadows.
There was no internet (heck the only computers around were at Boeing and IBM) and I'd never heard of fanfic or a Mary Sue.
My first stories were written with a buddy and they are now long lost (Thankfully - Spock really should be an only child).
The earliest work I still have is a Star Wars novel (before Revenge of the Empire, when even the Sci-Fi mags were speculating that Luke and Leia would get together and Darth Vader was the villain and NOT Luke and Leia's father.) I might, someday, get the courage to post in on the internet.
