Retroactive payment

I assume you're describing widow's benefits, which can be payable as early as age 60 (50 if disabled).

It may be possible to apply for survivor benefits retroactively, but I suspect it may not bear fruit unless you suspect you may have limited longevity.

If you begin receiving survivor benefits at age 60, then your monthly benefit will be reduced. By waiting until age 62 to receive survivor benefits, you'll receive a higher monthly check.

You can receive widows or widowers benefits based on your age at any time between age 60 and your full retirement age as a survivor. However, if you start at an earlier age, your survivors benefits are reduced a fraction of a percent for each month before your full retirement age. Your full retirement age is 66.

See the following :

http://www.ssa.gov/survivorplan/survivorchartred.htm

http://www.ssa.gov/survivorplan/1945s.html

If you started receiving survivor benefits at age 60, you'd receive 71.5 percent of the "full" amount (at age 66). If you begin benefits at age 62, you get 81 percent of the "full amount".

Contact the SSA for your particular case.