For certain school's specific aid, much like for the FAP through AMCAS, they don't care about your independent status or age, they want your parents financials. For the FAP you can somewhat contest this if you literally are not in contact with your family and thus wouldn't be able to provide their info. Perhaps most schools who do this also have such a form, but I'm not the kind of person to play that game when it isn't true, so I contacted my family and had them log in with their FSAID and fill out their portion of my FAFSA.
As for my particular school they say my parents information and my EFC value would not be used to determine any loan amounts, it would only qualify/disqualify me from any need based aid. From my meeting with financial aid personnel their stance is understandable:
Since the majority of people going into medical school are college-aged kids who have spent the previous years not working and just going to school, the FAFSA becomes less valuable as a tool to gauge people's actual need. As an example, I am 29, have lived the majority of my life under the poverty threshold, including my time in undergrad and my parents combined have made less than the average income of a single household during that time.. compared to a 26 year old who's family represents the average med-school matriculants, they could make their FAFSA look exactly like mine since they could refuse to provide their parents information.
So really it's a system that's designed for me, I just don't really appreciate having to fill-out the forms the way I had to, even if they were simply designed like that so their usual demographics can fill them out easily. As someone who's had to fill out their own FAFSA without their parents for my entire undergrad, it just seemed a bit off. I ended up with an EFC of 0 anyway, so I'll likely qualify for whatever need-based aid they can provide.
