"Proposals to raise the Social Security age often have the potential of hurting the poor. Wealthier people tend to live longer. As a result, they draw benefits for more years after they stop working until their deaths. Increasing the retirement age by the same amount for everybody could actually result in poorer retirees receiving benefits for a shorter period of time.
The details matter, though. As Andrew Biggs of the conservative American Enterprise Institute has argued, raising the retirement age might result in more Americans applying for disability benefits, because there will be several more years in which they might be injured or fall sick before they reach retirement age. Those disability benefits might make up some of the gap between rich and poor in welfare for elderly workers.