My first dev project was making a small 3D engine in GameMaker 7 when I was 14. I had been using gamemaker for two years then but I never got past the "platformer movement and collisions" and "top down movement and collisions"

It was the first thing I made myself without following a tutorial and spend quite a few afternoons at school to ask my Math teacher to explain things like sin cos and tan. Words I saw on the internet but did not understand.