查了下，如果是大点的公司，不会强行要求员工用medcare：

Generally, if you have employer-sponsored health insurance as a working individual over 65, you may not need to enroll in Medicare right away, but it depends on the size of your employer. If your employer has 20 or more employees, you can usually delay enrolling in Medicare Part B without penalty as long as you have active employer coverage. You may still want to consider enrolling in Part A, especially if it's premium-free, as it can offer additional coverage.