If your company plan has 20 or more members, you can delay Medicare enrollment without penalty. You should compare your options, as Medicare may be better coverage than your employer's plan.
Always check with your employer to be sure your coverage allows this.
If your company plan has less than 20 employees, Medicare will be your primary health insurance. You can enroll 3 months prior, and no later than 3 months after your 65th birthday.
If you miss this window you can be penalized by Social Security and may be ineligible for Medicare Supplement Plans.
This guide is meant to be for learning purposes only. There can be unique situations that need to be considered when going on Medicare.