As I understand it, you must sign up for Medicare at 65 years of age. When you trigger Social Security has nothing to do with signing up for Medicare. In fact, if you sign up for SS before age 65, you'll automatically get signed up for Medicare when you turn 65. Folks here will correct me I'm sure if I'm wrong, but this is how I understand it.
I’m 72 and still working. Because they automatically signed me up at 65, I did not know I was in Medicare. Last year my employer offered the Health Savings Account (HSA) which I signed up for. 10 months in they told me that I was inelgible because I was in the Medicare system even though I was on my work healthcare system. I had to repay all the copays and other medical bills that I used the HSA for and then I had to pay the income tax on it to boot. Writing a check for $2K was hard.
I signed up for Medicare Part A, required; I am working and will be covered by company provided insurance until about age 70. Won’t sign up for other coverage until then.
I was NOT required to sign up for Medicare & I did NOT do so.
Now 78, and have had only one instance where I could have used it. Cataract surgery. Got a decent CASH price from the doc. Paid Cash.
Medicare Part A is automatic at age 65. You can delay Part B and Part D after age 65 without penalty if you are still working and you are covered under a qualified employer-sponsored plan.