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The concept of a “retirement age” is becoming irrelevant, at least according to a new study of middle-class Americans.

Whether it's a desire to reach a certain nest-egg number, dealing with rising health-care costs, or grappling with mortgage debt, more workers are deciding to delay retirement.

A quarter of middle-class Americans — defined as earning between $25,000 and $99,000 annually — say they will “need to work until at least age 80,” according to the annual retirement study by Wells Fargo

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"Another interesting shift in the mindset of Americans is their perception of how much money they need. Three-fourths of respondents said it's more important to have a specific amount versus a date: $350,000 was the median nest-egg goal, but median retirement savings were only $25,000 dollars," said Laurie Nordquist, executive vice president of institutional retirement at Wells Fargo.

Money managers will tell you that the driving force behind delayed retirement is the savings gap. The gap is widened by grim economic factors hitting the middle class.

"Social Security cuts and mortgage debts are on the top of their minds," adds Nordquist.

Mortgage Debt

When it comes to mortgages, the generational gap is the great divider. Overall, 86 percent of respondents said they want to pay off their mortgage before retirement.

Get underneath the ages, however, and the tunes change. Ninety-one percent of people age 25 to 29 cited this goal as very important. Over age 60? Just 40 percent said they thought it was important.

This data reveal a growing trend in expectations. Much of them have to do with how young and old view Social Security .

Social Security

More than a quarter of people in their 20s and 30s expect no income at all from Social Security during retirement years. On average, people in that age group expect Social Security to cover only 20 percent of their retirement funding, according to the study.

While political leaders consider potential cuts to future Social Security and Medicare benefits, those already in their 60s still consider their pensions a sure bet.

Given these factors, what is a hopeful retiree to do?

"We're seeing people work longer, but they can also change their lifestyle expectations," Nordquist says.

Workers are already adjusting to this new reality.

"I'm talking with the tax man now to see what the options are. I wasn't planning on delaying retirement, no. But I'm considering part-time work," says Linda Wilson, 63, who works full time for the Bonnier Corp. She's been working full time for more than 20 years.

Inheritance? A Thing of the Past

The study also found that older Americans are hanging on to their money. Only 22 percent  of respondents said it was important to leave an inheritance.

Though economists pontificate about a massive wealth transfer between generations as the baby boomers age, in a struggling middle class, reality may disappoint.