The baby boomers are turning 65 every day and more of them are working longer in order to make ends meet. I enrolled one woman who was still working at 71 as a nurse in a maternity ward.
If you are still covered under your group health insurance you do not need to enroll in Medicare Part B until you actually leave the employer group plan (not using COBRA though). If you leave employment after age 65 then you do need to enroll in Medicare Part B, which in 2022 is $170.10, and will most certainly be going up next year.
Although you need to enroll in Part B, you have many options for Medicare coverage after that. You may enroll in a Medicare Advantage plan - which are either PPO's, POS', or HMO plans. Also available is a Medicare Supplement plan which has no network. These plans usually range from $50 - $200 and beyond. Although these plans are more expensive than Medicare Advantage plans, you have the ability to go to any doctor that you desire (as long as they accept Medicare).
Part D prescription plans are usually included in Medicare Advantage plans, but must be purchased separately if a Medicare Supplement plan is chosen.
Special enrollment periods allow Medicare beneficiaries to enroll in a plan outside of the annual enrollment period and include such things as moving, coming off of an employer group health plan, turning 65, coming off/on low income assistance, and quite a few other instances. Different states also have different rules on when you can enroll into a Medicare plan. Contact me if you have any questions about Medicare rules and regulations. The "Medicare and You" book from CMS is 82 pages long. If you do not have the interest in reading and understanding all 82 pages, definitely send me a message.