Once your 60s arrive, it's time to get serious about retirement -- especially since that milestone may be just a few years away. But part of setting yourself up for a secure retirement means avoiding these mistakes that could really set you back financially.

1. Claiming Social Security early

Your monthly Social Security benefit is derived based on your earnings record -- specifically, your 35 highest-paid years on the job. From there, you're entitled to your full monthly benefit at full retirement age, which is either 66, 67, or 66 and a certain number of months, depending on what year you were born.

That said, you're allowed to file for Social Security as early as age 62, and many seniors opt to go this route. But for each month you claim Social Security ahead of full retirement age, your monthly benefit is reduced on a permanent basis so that all told, you'll be looking at a 25% to 30% hit if you sign up at the earliest possible age.

Older man and woman taking a walk

Image source: Getty Images.

Of course, claiming Social Security early is tempting. If you file before full retirement age, you'll have more flexibility to spend. You can pay for the home improvement you've been putting off, or take the big trip you've been hoping for. But taking benefits early also means slashing them for life, and while the extra money may be nice initially, there's a good chance you'll come to regret lowering your benefit when your healthcare expenses start to mount, which tends to happen as people age.

2. Tapping your retirement savings too soon

Once you turn 59 1/2, you're entitled to take withdrawals from your retirement savings -- and you don't actually need to be retired to do so. But if you're still working, it really pays to leave that money alone. As is the case with claiming Social Security early, tapping your retirement plan in your very early 60s gives you more immediate options to spend. But down the line, that could really come back to bite you, especially when you start relying heavily on your savings to pay your retirement expenses.

3. Delaying Medicare

Your initial Medicare enrollment window spans seven months, beginning three months before the month of your 65th birthday and ending three months after that month. If you're still working at age 65 and are covered by a group health plan through your employer, then you have the option to stay on that plan and sign up for Medicare during a special enrollment period later on. But if you don't have group health coverage and you delay your Medicare enrollment, it could end up costing you in the long run.

For each year-long period you're eligible for Medicare but don't sign up, you'll have a 10% surcharge tacked onto your Part B premiums. Given that those premiums tend to increase from year to year anyway, that's not an expense you'll want to bear.

The moves you make in your 60s could spell the difference between a comfortable retirement and a miserable one. Avoid the above mistakes, and you're more likely to fall into the former camp.