I started collecting social security at 64 years old. Throughout my more than 40 working years i always paid the maximum FICA each year.
After retiring from my full time job at age 64 and starting to collect at that time, I worked part time with FICA taken out.
My question is why are these FICA contributions not adding to my retirement age with benefit increases that go along with it?
Can i opt out of paying FICA if i get no additional benefit from paying into it?

Hi. Social Security retirement benefits are based on an average of a person's highest 35 years of Social Security covered wage-indexed earnings, so additional years of earnings that a person has after they start drawing benefits only increases their benefit rate if the earnings higher than in one or more of the 35 years currently being used to calculate the person's benefit rate.

And, no, you can't opt out of paying FICA/Social Security taxes on your earnings even if those earnings won't increase your benefit rate.

Best, Jerry