Who is eligible for Medicare Part A?

Medicare Part A is generally available to individuals who are 65 years and older, as well as to certain younger people with disabilities or specific health conditions. Among the options provided, individuals who are retired at age 66 are indeed eligible for Medicare Part A, as they typically qualify once they reach the age of 65, provided they've worked and paid Medicare taxes for a requisite number of quarters.

Other groups may qualify for Medicare Part A before age 65, such as those with disabilities or End-Stage Renal Disease (ESRD), so while these individuals might also be eligible, the primary and most common eligibility is based on age and retirement status, making option B the correct choice. The eligibility criteria will apply universally regardless of employment status or age below 65, but the option emphasizing retirement at a standard age captures the essence of Medicare’s primary guidelines.