As of 2015, most U.S. citizens and permanent residents become eligible for Medicare at age 65. People who wish to receive Medicare should sign up approximately three months before their 65th birthday.
In order to be eligible at 65, a person or his spouse must either receive or be eligible to receive Social Security benefits, receive or be eligible to receive railroad retirement benefits, or have worked long enough in a government job where Medicare taxes were paid. Parents 65 and older of a fully insured deceased child also become immediately eligible for Medicare.
If under 65, a person can apply and receive Medicare if he has a disability and has been collecting Social Security disability insurance for at least 24 months. Any person who is diagnosed with multiple sclerosis, end-stage renal disease or kidney disease also becomes eligible to apply and receive Medicare and Social Security disability benefits before age 65.