SS is actuarially neutral for an individual. Excluding most all other outside factors, it makes little difference when to start SS. Once you start including those outside factors and plans, there are significant differences. For example, a married couple's survivor's benefits, assuming a fair difference between earnings over their lifetime, certainly swing the pendulum into favoring delaying. That is, if you can afford to delay. That is because the average life expectancy of the last survivor of a couple is greater than an individual, which the SS does not consider in their numbers AFAIK. Another example is women. While it is generally accepted that the average woman lives longer than the average man, the SS doesn't differentiate in their calculations. Women, based on just being women, will automatically live longer than the SS's breakeven age.
In the end, we don't know when we will leave this earth (or become parts of it), what the market will do in the mean time, or any number of other variables. 100% accurate numbers cannot be calculated. We must take a few wild guesses and punt. When it comes down to individual experieinces, averages do not apply.