Most people first become eligible for Medicare at age 65. If you're already receiving benefits from Social Security or the Railroad Retirement Board, you'll automatically be enrolled in Medicare Part A (hospital insurance) and Part B (medical insurance). You'll get your red, white, and blue Medicare card in the mail about three months before your 65th birthday. If you're not receiving benefits from Social Security or the Railroad Retirement Board, you'll need to actively enroll in Medicare.