There is no such thing called eligibility criteria or the age limit in the GRE test but there are a few things to keep in mind.Fundamentally, the applicants are expected to have an undergraduate degree or prospective graduates are also eligible to apply.
Once an applicant takes up the exam and gets the resulting GRE scores, he is expected to apply for the universities or business school on their own.
This implicitly requires the aspirant to meet certain eligibility criterion, qualification, and other norms set by the desired educational institution. So the aspirants should be thorough with their selection of universities or business school beforehand and make sure that they are eligible for the same.
The GRE test is mainly conducted for admission into graduate level, post graduate level as well as doctoral programs.