This isn't too big, but it was big for me.
I was on a school trip to place X, it was a math competition. I was in grade 8.
The kid whose family hosted me and my friend for the competition was in 10th grade. One night, we were playing on the PS4 when he went off to work. Turns out he had to make a website for a technology assignment. I looked at it, and told him, "What's this? Looks easy. Really easy." I'd done a similar thing in grade 6. When I told him he asked me to show him the website. I downloaded it off Google drive(where I keep it) and showed it to him.
It took me a couple of minutes to convince him that I'd made in grade 6. Made me so happy :)