You know the old mantra: When you turn 65 you are eligible for Medicare and Social Security. But matters are no longer that simple. And because growing numbers of older Americans are not taking Social Security benefits until past 65, they may be making poor Medicare choices or missing out on some benefits entirely–simply because the government is not telling them they need to actively enroll for health coverage.

If you are already collecting Social Security when you turn 65, getting Medicare is relatively simple.  When you signed up for your Social Security annuity payments (as early as age 62), you also did the paperwork to start getting Medicare at 65.

But for the Baby Boomers, full retirement age is no longer 65. It is 66 and beyond. Thus, many older Americans are not taking Social Security at 65. Many are still working and receiving health insurance from their employers. Others are enrolled in the Affordable Care Act health exchanges or in the expanded Medicaid program. Millions of people in these situations will not automatically start getting Medicare benefits on their 65th birthday. They need to take steps to enroll, and don’t know it.

And it isn’t simple stuff. There is a an Initial Enrollment Period, a General Enrollment Period, a separate enrollment period for Medicare Advantage, and a special enrollment period for people who have big life changes.

It gets even more complicated if you are making a transition from ACA marketplace insurance or Medicaid at age 65, or if you have COBRA coverage or are in your employer’s retiree health plan.

If you’re still working at 65 and getting employee health insurance from a larger firm you may want to delay enrolling in Medicare Part B. But you may want to take Part A hospital insurance. You pay no monthly premium for Part A but still have to enroll (you can do it pretty quickly online). Unfortunately, unless you are already getting Social Security benefits, you may not be aware that this should be at the top of your to-do list.

As your 65th birthday approaches, you’ll start getting marketing materials from private insurers who are peddling Medicare Supplemental (Medigap) insurance, Medicare Part D drug insurance, or Medicare Advantage managed care plans. But if you are not already receiving Social Security benefits, you won’t hear a word from the government.

Medicare enrollment information is available on the website. It even has a section on what to do if you  want to enroll only in Medicare and not start Social Security benefits. The problem is, you have to know to look, and I suspect many people don’t.

Because of this odd information gap, many will lose out on months of Medicare coverage. Some may even have to pay lifetime premium penalties because they missed key enrollment dates.

This could be easily fixed. The government could send Medicare enrollment notices to everyone three months before their 65th birthday.  Those notices could explain what to do if they are not already receiving Social Security benefits.

Why don’t we get such basic information already? Mostly because the issue seems to be slipping through the bureaucratic cracks. The marketing people at AARP or Aetna can figure it out but the government, not so much.

Last week, a group of lawmakers urged the Obama Administration to clean this up, and provide notice and some basic information about Medicare eligibility for those turning 65 but not already collecting Social Security benefits. It’s a simple fix that government ought to make right away.