Source: Elder Law Answers
Medicare benefits start at age 65, but many people continue working past that age, either by choice or need. It is important to understand how Medicare and employer coverage work together.
Depending on your circumstances, Medicare is either the primary or secondary insurer. The primary insurer pays any medical bills first up to the limits of its coverage. The secondary payer covers costs the primary insurer doesn’t cover (although it may not cover all costs).