When you turn 65 you become eligible for Medicare and are asked to sign up. Medicare has a number of parts.
Medicare Part A primarily covers hospital care as well as skilled nursing facilities, nursing homes, hospice and some other services. There is no cost to the individual for Part A.
Medicare Part B primarily covers services (like lab tests, surgeries, and doctor visits) and supplies (like wheelchairs and walkers) to treat a disease or condition. There is a monthly charge for Part B.
If people choose to continue working after age 65 and if they are covered by a group health plan they may not sign up for Part B.
If they do not sign up for Part B at age a 65, they may be subject to a “late enrollment penalty.” According to Medicare.gov
Your monthly premium for Part B may go up 10% for each full 12-month period that you could have had Part B, but didn’t sign up for it.”
However, this penalty does not apply of you can prove that you had medical insurance coverage for the time you declined the Part B.