I believe they are exhibiting denial that YouTube could possibly be old enough to have videos uploaded 18 years ago.
This denial is being done mostly in jest to cover the true, creeping, dripping, existential despair that so much time has passed, but at the same time to commiserate and laugh with others who are similarly affected. Drip, drip, tick, tick, tick.
Also, the video turns 19 in a couple of months. yaaaaay
Sorry, I never meant to imply you were stupid. Only that you didn’t seem to be of a high enough technical level - right now - to be able to solve your PC problems.
As for (non-committal) further advice: Backups, backups, backups. And then a tool like WinDirStat to track down what’s using all your space. There are YouTube videos that show you how to use it.