Any student who is planning to take an admission to graduate, business, and law school can take GRE. It is considered an important part of their application. Having said that, a student must check the university or college website (that they intend to attend) to know the required score. Different universities or colleges have different score requirements. Unlike other standardized exams, this exam has no eligibility criteria.
Age: There is no specific age limit for GRE exam. A candidate of any age can attend the exam.
Exam Qualification: The ETS has not made any official statement about the eligible exam qualification. However, a graduate in any discipline can attend the test.
Score: This would entirely depend on your host organization. The ETS has set no minimum qualifying score for GRE.