Countless Americans plan for their golden years by aiming to lock in a retirement age and then working toward that goal. But unfortunately, many ultimately end up unsuccessful in retiring on time. Since 2008, only about half of working adults have retired on or close to schedule, according to the Employee Benefit Research Institute. And while a big reason boils down to money, there are other contributing factors, too.

If you have your heart set on retiring at a specific age, be careful -- there are several reasons why things may not work out that way in the end. Here are just a few to be aware of.

Senior man walking by the water

Image source: Getty Images.

1. You don't have adequate savings

We're told time and time again that Social Security won't cut it in retirement and that it's on us to save for the future ourselves. Yet countless older workers are approaching retirement with nowhere close to what they need to sustain themselves for 20 years or more. The average household aged 56 to 61 has a $163,577 nest egg, according to the Economic Policy Institute, and while that's better than nothing, if we assume an average annual 4% withdrawal rate, which has long been the standard, that results in just $6,543 a year in income. Throw in the average monthly Social Security benefit, which is roughly $1,360, and all told, you're looking at less than $23,000 a year to live off.

Furthermore, while $163,577 represents the average savings balance among older workers nearing retirement, the median savings for that age group is a mere $17,000. At a roughly 4% annual withdrawal rate, that sort of nest egg would leave you with a paltry $680 a year in income on top of whatever Social Security pays you.

If your savings balance mimics either of the above figures or falls somewhere in between, then there's a good chance you'll end up having to retire later than planned so that you can bank some extra cash for the future and stretch what limited dollars you've amassed so far. The good news is that come 2018, older workers with a 401(k) can sock away up to $24,500 annually. Do that for a year or two, and you'll be in much better financial shape for retirement.

2. Your investments are too conservative

Building a strong nest egg isn't just a function of setting money aside during your career; it's also a matter of investing that money wisely. Unfortunately, 60% of workers invest too conservatively for retirement, which means that rather than focus on maximizing gains, they instead go out of their way to avoid losses. But if you're doing just that, there's a good chance you'll end up needing to postpone retirement when your savings balance isn't what you need it to be.

The following table shows how your nest egg might suffer if you adopt too conservative an investment strategy:

Investment Style

Average Annual Investment Return

Total Accumulated Over 30 Years (Assumes a $400 Monthly Investment)

Aggressive

8%

$544,000

Moderately aggressive

6%

$379,000

Moderately conservative

4%

$269,000

Conservative

2%

$195,000

Table and calculations by author.

You can't help but notice the difference between an 8% average yearly return, which you're likely to get with a stock-focused portfolio, and a less aggressive number. The takeaway here is that if you play it too safe with your savings, you could wind up in the same position as someone who neglects to set money aside in the first place. And in either scenario, retiring on time is unlikely.

3. You enjoy working and don't want to give it up

Even if you're actually looking forward to retirement, there may come a point when you realize you're just not ready to leave your career. This is especially likely to happen if you enjoy your work and have enough energy to keep at it. In fact, in a recent Capital Group study, 22% of baby boomers intentionally pushed off retirement because they realized they still liked their jobs and wanted to stay.

It's no secret that retirement can be a tricky adjustment for those used to working full-time, but what you may not realize is that leaving the workforce actually increases your likelihood of falling victim to depression by 40%. You may therefore come to find that as your expected retirement age nears, you're just not ready to pull the trigger. And there's certainly nothing wrong with that.

No matter why you might end up retiring later than planned, the key is to roll with that change and learn to embrace it. With Americans living longer these days, there's a good chance you'll come to enjoy many good years of retirement -- even if you have to wait a bit longer to get there.