I’m < 2 years away from what I believe is mandatory Medicare. I don't believe it's mandatory. Googled and found this:
According to the Social Security Administration, Medicare coverage is mandatory at age 65 only for
employees of state and local governments who were hired or rehired after March 31, 1986.
I also know I had free healthcare coverage when I retired from my employer and it had nothing to do with Medicare.
Unfortunately, the company dropped it the year I retired (luck of the Irish).
I only know what my slightly older cousin and my internet search found. If you don’t take Medicare, many insurance companies drop you at 65. I work part time and get my insurance through my husband. He’s a year younger and works for a large company. Chances are good my cousin is correct as her husband worked for a large company before retirement.