I am 66 years old, work for a large employer, and have excellent health insurance coverage through my job. I am planning to keep working for a few more years and would like to keep the coverage that my employer offers. How does the Marketplace affect me?

It doesn’t.  You can keep your employer-sponsored health insurance coverage as long as that is an option for you.  Since you are already eligible for Medicare because you are over age 65, you should sign up for Medicare when you stop working or if you lose your employer coverage before then.  Once you decide when you want to stop working, you should contact the Social Security Administration about how and when to enroll in Medicare to be sure you don’t have a gap in coverage.