I learned on the internet 15-20 years ago or so. I've also done 5x5 and 4x4 they aren't really much harder, I didn't need additional info, but when I hit the parity problem on the 4x4 I just scrambled and tried again. I mean they are harder, but not astronomically harder.

My almost 8 year old is obsessed. I went through how to do a 3x3, and wrote out the steps and he has copied my instructions into a notebook. He can do it in 3 and a half minutes with his notes. He hasn't managed without his notes yet but he has only been learning since Valentine's day. He just woke me up looking for his notebook.

Earlier this week I met somebody that did a Rubik's cube independently in the 80s. (My son's classmates grampa).