It's kind of weird though. Is VxWorks (a proprietary embedded OS used on some of the Martian rovers) going to require it in case some underage Martians try to use Facebook?

That depends. Will some kid be caught accessing Facebook from a Martian rover, triggering a court case? Remember, the law only cares about things that actually happen.

I'm sure they have a feature that also asks for species. Martians being longer lived than humans, they come of age at around 42.