You’re 18? I will assume, given Taiwan’s historical racial make-up, that you are ethnically Asian? I don’t know what cram school requirements are for Taiwanese citizens, but foreigners need at least an undergrad degree to get a work permit. It’s possible you can get a desk job or be a teaching assistant, but I think most cram school employees are, at minimum, currently in college/Uni or graduated.
You will also, if not white, run into the issue that potential employers probably don’t care if you’re a native English speaker, because your face doesn’t work well from an advertising standpoint. I know of a school in Taipei that hired the white, American husbands of Taiwanese women who had already worked in the school for years (and who had attended high school through Uni and up in the US) and then told the women they could go be office slaves or pound rocks instead of renewing their contracts. The school was very proud to brag that they “have at least one American teacher in each classroom”, even though the other (not husband) foreign teachers were from non-English European countries. It’s ALL about appearences