If you are 65 years or older, you still have to meet certain other eligibility requirements before you can enroll in Medicare. First, you have to be a United States citizen or a permanent resident who has lived in the U.S. for at least five years. In addition, you must meet one of the following eligibility requirements: You or your spouse has worked at least 10 years and are eligible for either Social Security or Railroad Retirement benefits. You or your spouse is a government employee or retiree who has paid Medicare payroll taxes while working. You can use the Medicare Eligibility Premium Calculator at Medicare’s website to find out if you are eligible for coverage.