If you did not enroll in Medicare when you originally became eligible for it, you can sign up during the General Enrollment Period, which is from January 1 through March 31 of every year.

Your coverage will begin July 1 of the year you sign up. You will have to pay a Part B premium penalty for every year you delayed enrolling in Medicare Part B.

ESRD

You can get Medicare no matter how old you are if all of these apply:

Your kidneys no longer work
You need regular dialysis or have had a kidney transplant
One of these applies to you:
You’ve worked the required amount of time under Social Security, the Railroad Retirement Board (RRB), or as a government employee
You’re already getting or are eligible for Social Security or Railroad Retirement benefits
You’re the spouse or dependent child of a person who meets either of the requirements listed above
Contact Social Security for more information about the amount of time required to be eligible for Medicare.

If you’re eligible for Medicare because of ESRD, you can enroll in Part A and Part B by visiting your local Social Security office or by contacting Social Security.

If you qualify for Part A, you can also get Part B. Enrolling in Medicare is your choice. But, you’ll need both Part A and Part B to get the full benefits available under Medicare to cover certain dialysis and kidney transplant services.

When you enroll in Medicare based on ESRD and you’re on dialysis, Medicare coverage usually starts on the first day of the fourth month of your dialysis treatments. This waiting period will start even if you haven’t signed up for Medicare. For example, if you don’t sign up until after you’ve met all the requirements, your coverage could begin up to 12 months before the month you apply.

If you’re covered by an employer group health plan, your Medicare coverage will still start the fourth month of dialysis treatments. Your employer group may pay the first 3 months of dialysis.

Medicare coverage can start as early as the first month of dialysis if you meet all of these conditions:

You take part in a home dialysis training program offered by a Medicare-certified training facility to teach you how to give yourself dialysis treatments at home.
Your doctor expects you to finish training and be able to do your own dialysis treatments.
The regular course of dialysis is maintained throughout the waiting period that would otherwise apply.

If you have Medicare only because of permanent kidney failure, Medicare coverage will end:

12 months after the month you stop dialysis treatments.
36 months after the month you have a kidney transplant.
Your Medicare coverage will be extended if:

You start dialysis again, or you get a kidney transplant within 12 months after the month you stopped getting dialysis.
You start dialysis or get another kidney transplant within 36 months after the month you get a kidney transplant.
Note

There is a great deal of information here.