It doesn't even need to be a degree, honestly. You could go learn a trade. There are many trades that pay much more than many white-collar desk jobs. I'd say check out your local community college, trade school, or similar to see if anything looks interesting. Contact them and request more information or even a tour if something does. Regardless of the route you take, you definitely want to learn some sort of marketable skill. Also, there's nothing wrong with pursuing a career that's just tolerable or boring, but pays the bills. You can seek fulfillment outside of work.

As far as not knowing what to go for at 21, I just worked after graduating high school at 18, and it wasn't until I was 23 that I decided to go back to school.