You (if male) have to register for selective service. If a male doesn’t register by age 27 (I think that’s it, I have 2 girls) it is very difficult to get it corrected. It is asked whether you are register on the federal job applications. If you registered and are female, it would just be dropped.
I did my kids’ FAFSAs too, because they were away at school. Sometimes I’d call them to ask questions and say “I’m hitting send” but not always. I did their taxes too because I needed the info to do MY taxes and take the AOTC. But even if they saw the FAFSA they would have seen my income. I used the DRT and the numbers were grayed out, even to me. I guess they could have seen my enormous bank account numbers…
Some don’t realize they qualify. My kids didn’t get anything the first semester, but I filled it out anyway. Because I had a big change in income (job ended) the schools advised me to file a change in circumstances and I did and they got Pell grants very late in the spring. I never filed for FA when I was in school because my father said we wouldn’t qualify. I’m pretty sure he was wrong as we were a family of 9 with 3 in college. If I knew then what I know now…
But if you don’t want to fill out FAFSA, don’t. You might be missing out on some grants (Covid money, a bonus just for filling it out (Stetson used to give them)) or if they are required for merit. Just ask your school if you have questions about the requirement.