Yes, as a non-degree seeking student. While there is no limit to the number of courses a student can take as a non-degree seeking student, normally these courses cannot be applied towards a graduate degree. For U.S. citizens and permanent residents, there is no official deadline. However, be aware that there are practical time constraints on the application process. The department does not set minimum required scores.
Financial assistance is competitive and test scores weigh heavily in that decision.
You should request three recommendations from individuals who are familiar with your academic achievement and potential. If you are unable to contact former professors, you may submit non-academic references, such as those from employers. Remember, however, you are being judged for your academic achievement and potential. The GRE scores are good for five years from the date your application reaches the Office of Admissions and Records. Those applicants whose native language is not English, with the exception of those having completed all four years of a baccalaureate degree in the United States or achieving a 400 Verbal GRE score.