This is relatively common in the military where being married bumps up your salary and gives your spouse free health care. One young lady I knew had her husband take out credit cards in her name. Also, IANAL, but prenups hold different weight in different states, no?
In the military, getting married to get paid more or to get off-base housing (a "sham" marriage) will get you jailed and dishonorably discharged. The housing allowance gained through the sham marriage is technically larceny -- it's a stolen benefit. [1] [2]
I would not be surprised if college kids in a sham marriage to gain financial aid could be charged with larceny of the financial aid.
Another, less felonious option, is to simply wait until you're 24 to start going to college full-time. Spend a few years going on some ridiculously interesting adventures, and another few years trying out various jobs, and you go to college as a mature adult with some actual life experience and a better idea of how you want to spend your life? I'm surprised it's not much more common. I guess if the cutoff was 21 and not 24 it would be an obvious choice, 6 years only works if you can actually start working in your industry of choice before getting the degree.
The military might have some luck with such regulations, but I doubt civilian bureaucracy even pretends to care as long as the marriage actually exists on paper. It's just not enforceable.
The military is one thing, but I don't foresee a time when DoE is going to able to comment on the "content" of a marriage. Realistically, most of the most significant benefits of marriage are financial. This is just another example of such.
