What do 18-24 year olds do if they want to attend college but their parents won't provide FAFSA information?

There is a process called a Dependency Override that permits an administrator at your school to change your status to independent. However, it can only be used for serious situations in which it would be unsafe or impossible to obtain parent information (such as a history of abuse, abandonment, incarceration, etc). School administrators are prohibited from using it for cases where a parent simply refuses to provide the information. This is because the federal student aid system is based on the premise that parents should pay for education to the best of their ability. The way that ability is determined is through the FAFSA, so if the parent will not provide information for it, then your eligibility for aid cannot be determined. If all a parent had to do to get around this was refuse to provide the info, then every parent in the country would do that and the system would be bankrupt overnight. For situations where a parent refuses to submit information for the FAFSA, the student can submit it without parent info. It will reject, but the school can then--at it's discretion--award an unsubsidized loan at the dependent level to the student. It's not required that they do this, and some schools won't, but it's worth a try. Your chances are better if you can obtain a letter from your parents stating that they refuse to provide information for the FAFSA, and that they are not providing support to you and will not provide support in the coming year.

Join the military.

You'll get away from home, earn a paycheck, have all your housing and medical needs met, learn some skills, get in shape (or better shape), and when your enlistment is completed, you can pay for school with your GI Bill benefits.

You CAN get a loan without your parent filing a FAFSA; however, you would not be eligible for a Pell grant or on-campus job. However, I urge you to be very careful about incurring a lot of debt to go to college.

From the source, below...

"If there is anything unusual about your relationship with your parents, such as a history of abuse or a hostile home environment, bring it to the financial aid administrator’s attention. Sometimes they can use this information to justify a dependency override. The college will want to see independent third party documentation of the situation, such as a copy of a court protection from abuse order or a letter from a social worker, teacher, clergy or guidance counselor.

If your parents still refuse to complete the FAFSA, the college has the authority to make you eligible for unsubsidized Stafford loans without parental information on the FAFSA. Section 472 of the Higher Education Opportunity Act of 2008 amended section 479A(a) of the Higher Education Act of 1965 to permit college financial aid administrators to offer dependent students unsubsidized Stafford loans “without requiring the parents of such student to file the financial aid form prescribed under section 483 if the student financial aid administrator verifies that the parent or parents of such student have ended financial support of such student and refuse to file such form”. This won’t make you eligible for a grant or work-study, but at least it is something."

contact FAFSA and see if there are any options for people whose parents won't cooperate

You get a part-time job and pay for school on your own. Go to your closest community college, even going full-time should run $5000 a year or less.