I had created two languages from scratch by the time I was 15. One kind of sucked. That was my first attempt.
But the second one was well thought out and pretty cohesive; it couldโve been used by actual humans. Hell, it was used by me. I kept my class notes in it for over a year. Turns out, though, teachers get upset when you hand in a notebook in a language ainโt nobody ever seen before and only one person in the world can read. Heh.
Iโm pretty proud of that. Not annoying my instructors, but rather creating my own language de novo with very few outside resources. Just my own big fuckinโ brain and the will to do it.