The rules are quite clear and linked on the page but if you can't be bothered:
> GSoC Contributors.
> Eligibility.
> Requirements. To participate in the Program, a GSoC Contributor must:
be eighteen (18) years of age or older upon registration for the Program;
for the duration of the Program, be eligible to work in the country in which they reside;
not be an Organization Administrator or Mentor in the Program; and
be a student or a beginner to open source software development.
> GSoC Contributors.
> Eligibility.
> Requirements. To participate in the Program, a GSoC Contributor must: be eighteen (18) years of age or older upon registration for the Program; for the duration of the Program, be eligible to work in the country in which they reside; not be an Organization Administrator or Mentor in the Program; and be a student or a beginner to open source software development.