How to self-educate if you’re young:

1) Read any and every book an adult tells you is “too advanced for you” or where an adult says anything about the work like “you shouldn’t be reading that at your age.”

2) Start reading undergrad textbooks and such as early as you can understand 50% of what’s in there. Look up what you don’t. (This is much easier in the age of the internet, though I expect that’ll be taken away soon enough.)

3) Find a mentor to help you learn what to ignore (hint: most of school) and what to study intensively.

4) Establish a firm base of philosophy. This helps you with all else — even (and especially) STEM.

5) If there is anything separate of point 1 above that an adult tells you that you should not be studying, concentrate on that very damn closely.

This is pretty much what I did and how my brain got so damn big.