According to WebMD, the majority of individuals who are eligible for Medicare are 65 or older. Individuals with kidney failure, Lou Gherig's disease, or other disabilities or illnesses that prevent them from working are also eligible.
WebMD explains that Social Security recipients are automatically enrolled in Medicare at age 65, while individuals not yet receiving Social Security need to enroll three months prior to turning 65. Those diagnosed with Lou Gherig's disease, regardless of age, are also automatically enrolled. There is a three-month waiting period for individuals with renal failure, and a two-year waiting period for those receiving Social Security Disability for other health issues.