There is no gain to waiting beyond age 70 to file for your retirement benefits. You can retroactively collect up to 6 months of post age-70 retirement benefits without permanently reducing your retirement benefit. For example, if you are 71, you can collect your retirement benefit starting at 70 and 6 months. If you are 70 and 4 months, you can collect your retirement benefit starting at 70 without having it reduced permanently, which would happen were you to collect benefits retroactive to age 69 and 10 months (i.e., 6 months before your current age).