I am also a high schooler, and in the future I also want to start a game company.
I also love the sao world, so we’re quite alike.
Here’s my two cents. First off, start out small. VERY small. Make a couple o’ products, just little things that show off what you can do and get you to understand how stuff works after release and such.
Your idea may be awesome, but as I say “a developer’s first game will always fail”. Now, that would suck if your first game was your dream game, cause then it would most likely fail! 
xD
Even better, use the same code again and again, making them more complex, after every “release”. In other words, find some sort of way to release something. ANYTHING. This is key.