Is there a way I can declare myself as an independent (meaning my parents don't claim me as a dependent on taxes and stuff like that)? I'm not quite sure how it exactly works. I've heard I'm automatically considered independent once I turned 18?

The reason I want to do this is because my mother is disabled and is on medicare, and my father says that even though I'm 21, I can't get a job or else medicare won't cover her medical costs. First off, is that possible, because I'm slightly reluctant to believe my dad sometimes because he's really strong on the importance of education and really wants me to get my bachelors degree before getting a job...sounds really unorthodox nowadays since most people are getting jobs when they turn 16. So I thought if I declare myself as an independent, then I would be able to get a job without my mom losing her coverage. Also, I'm definitely going to be going to school full time, but just want some extra cash and some job experience.

Anyways, I'd appreciate any advice/answers you have.
Also, please excuse any ignorance I may have portrayed!
Thanks.