As a general rule, there are only two qualifications to determine if someone is eligible for Medicare coverage: first, if the person is 65 years of age or older; second, if the person has been a legal resident of the United States for at least five years. However, there are also allowances for people with disabilities who are under the age of 65.
If you have been working in the United States for more than ten years and as a result have paid Medicare taxes off of your payroll for at least the last ten years, you not only qualify for Medicare coverage in general, but additionally all the premiums that you would normally pay under Medicare Part A are entirely waived. This is definitely worth checking with Medicare to see if you qualify.
One final note is that people who qualify from Medicare may also qualify for Medicaid, if they make below a certain income each year and otherwise meet the requirements of Medicaid.
Some states even will allow Medicaid to pay the Part B premium under Medicare, in addition to some other medical or hospital expenses that may arise. Again, it is vitally important to check with both your state and federal agencies to determine whether or not you qualify for this heightened benefit, as it can provide significant cost savings that are particularly beneficial if you have limited means.