Social Security wages in box 3 of your W-2 is not money that you receive from Social Security. It's part (or all) of the wages that you earn for working, and you have to pay Social Security tax on it, no matter how old you are.
The benefits that you receive from Social Security are shown on your Form SSA-1099. You do not pay Social Security tax on your Social Security benefits, but depending on how much income you have you may have to pay income tax on part of your Social Security benefits.
