According to Coronado's paper, while that could improbably be chalked up to "individuals (who) are so cautious that they oversave and find themselves in a surplus position at older ages (a view refuted by a large body of data and research)," Coronado wrote, "there is something else afoot."

That something else includes a job market that is distinctly unfriendly to older workers, forcing them out earlier than they had planned and reluctant to hire them for anything but part-time jobs. It also includes other unforeseen circumstances, such as ill health and the need to care for a relative. And people are not planning for these contingencies.

The author cites numbers from the Retirement Confidence Survey conducted by the Employee Benefit Research Institute that indicate a steady rise in the number of people who plan to retire after age 65. In 1991, only a little more than 10 percent planned to linger in the workplace past 65; now that number has risen to approximately a third.

But people are retiring earlier rather than later; only about 15 percent stay past age 65.

Those who retired earlier than they'd intended gave reasons that implied their standards of living in retirement took a hit. Twenty-two percent cited downsizing or firm closure, while 61 percent said they left due to health issues or disability and another 18 percent said they had to care for a family member.

Coronado wrote, "The implication is that workers must factor considerable uncertainty about their ability to work later in life into their planning process, rather than assume they can work as long as they want."