CNBC's Kelly Holland takes a closer look at what's causing a number of retirees to leave the workforce much sooner than they expected, and how younger​ generations, like millennials, are preparing for their own retirement—​perhaps even better than those who came before them.

According to a new report by the Transamerica Center for Retirement Studies, two-thirds of workers over the age of 50 expect to work past 65 However, that expectation may not quite match reality, as the current median age of retirees was  62. Two-thirds of those current retirees  ​didn't leave the workforce by choice, but due to reasons like job loss, reorganization, or a company buyout. Due to the early leave, they're often left with limited nest eggs. The center found a median savings of $135,000 for the same group​.

Millennials, by contrast, appear to be doing more to prepare for retirement. Some 68 percent are currently saving for retirement, according to a recent study by the Insured Retirement Institute and the Center for Generational Kinetics. That is an improvement on the 64 percent of workers aged 50 or older who told the Transamerica Center surveyors they were doing so.

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