Social Security was designed to replace income once people could no longer work. In the 1930s, the retirement age was set at 65, which coincided with the age used by many private and public pension plans. In the late 1950s and early 1960s, Congress changed the law to enable workers to claim benefits as early as 62. But benefits claimed before 65 were actuarially reduced, so that those who claimed at 62 and those who claimed at 65 could expect to receive about the same total amount in benefits over their lifetimes.
Read the full report via the Center for Retirement Research at Boston College: IB_13-15-2