I think you talk about "Medicare Eligibility" here and the post from another person earlier was talking about some misunderstanding people have about "Medicare Benefit"
"Medicare Eligibility" is for every US citizen above 65 or with some disabilities and also for every legal resident after 5 years of residency.
"Medicare Benefit" from the government is for people who pay payroll tax and accumulate enough points so that the government pays for most of the premium cost.
The difference is in the premium and benefits. Usually people don't get enough points will need to pay about $700s-900s/month to buy both Part A and Part B once they become eligible and have higher deductibles too. Most Chinese seniors here don't buy Medicare out of pocket because they can't afford it.