Which of the following is a factor for Medicare eligibility?

Medicare eligibility is primarily determined by age, and one of the key criteria is that individuals must be 65 years or older. This age requirement acknowledges the increased healthcare needs typically associated with older age and aligns with the program's goal of providing medical assistance to senior citizens.

Additional criteria for eligibility can include disability status and specific health conditions, such as End-Stage Renal Disease or Amyotrophic Lateral Sclerosis, but the age criterion stands out as the most universally recognized requirement for enrollment in Medicare. The other factors listed, such as age under 65 or income levels, do not fulfill the eligibility requirement for Medicare in the same way.