But if you are not yet collecting Social Security benefits, you will have to sign up yourself by visiting: ssa.gov/benefits/medicare to enroll.
Whether you need to do that right away depends on what kind of health coverage you have when you turn 65. If you have a retiree insurance plan or COBRA or enrolled in an Affordable Care Act plan, you need to get on Medicare Part B, if you don't enroll in Part B by the end of the third month following your 65th birthday, you will be subject to a late-enrollment penalty that will increase your premium for as long as you are on Medicare.