There is no eligibility criteria or the age limit as such for the GRE test but there are a few necessary things to consider.
Fundamentally, the applicants are expected to have at least an undergraduate degree, but prospective graduates are also eligible to apply as the GRE scores have the validity of 5 years. This implies the applicant has to be at least 18 years old. Once an applicant takes up the exam and gets the 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 the selection process of universities or business school beforehand and make sure that they are eligible for the same.
The applicant can choose which universities or fellowship sponsors he/she wants to receive the scores. As part of the test fee, one can designate up to four score recipients. If the applicant prefers to send score reports later or wants to send score reports to more than four recipients, then they can send additional score reports for an additional fee.
Since the identification(ID) document required to write the GRE test is the passport, the applicant must have a valid passport of their host country.
The GRE test is mainly conducted for admission into graduate level, postgraduate level as well as doctoral programs.