The ultimate American dream used to be to get rich young and "retire by 40." Now the goal for the rich is to retire past 70—if they retire at all.

A new survey shows that America's highest earners don't plan on retiring until they are at least 70 years old. Lower-income groups—and even those considered "affluent"—plan to retire much younger, according to the study from Spectrem Group, a wealth research firm.

When asked "At what age do you expect to retire?" nearly one-third of those with annual earnings of $750,000 or more answered "over 70." Fifteen percent of them say they never plan to retire.

(Read more: What is rich? Study takes a crack at the answer)

On the other hand, only 6 percent of those making under $100,000 a year plan to retire after 70, and the same percentage say they never plan to retire. Most plan to retire by 65.

The Spectrem survey is backed up by other, previous studies. A 2010 study from Barclay's Wealth found that 54 percent of millionaires say they want to continue working in retirement. Globally, 60 percent of those with a net worth of $15 million or more plan to stay involved with work "no matter what their age."



The numbers contrast with the popular notion that Americans are retiring later mainly because they can't afford to stop working. The Spectrem survey shows that the highest earners—and those who can best afford to retire—are actually working the longest.