According to a working paper issued by the National Bureau of Economic Research, absent adjustment for higher life expectancies, the percentage of the U.S. population eligible for full Social Security benefits will climb by 2050 to about 20%. In "Adjusting Government Policies for Age Inflation", economists John B. Shoven and Gopi Shah Goda find that historical adjustment of eligibility ages for age inflation would have increased ages of eligibility by approximately 0.15 years a year.
The authors state that, at the time Social Security was created in 1935, an average 65-year-old retiree could expect to live just over 12 additional years; however, by 2004, an average 65-year-old could expect an additional 19 years of life. Accounting for higher life expectancies, "the Normal Retirement Age for Social Security in 2004 would have to be at least 71…and more likely 73 or 74" to be consistent with the retirement age of 65 in 1935, the authors wrote.
Source: Wall St. Journal Blog "Economists Warn of Effects of Age Inflation" (August 19, 2008)