I am going to go with you playing the default age settings. I have added to mine but the outcome would be the same. When my sim reached the elder stage, instead of the regualar count down, 21 days, 19 days, and continuing until they reach the set life span for elder of 21 days, it was the reverse.
Instead of showing 21, it showed the total of her life at that stage, so she was 175 at her life span. I had given the elders 21 years, each day it went up, 176, 177, and so on. When she readed the 21 day set (196), she continued and she "ended" at 209. Her hubby had been five days younger than her, but he died at age 201.
Guess it goes to show that women live longer than men not only in real life but in sim life also.
(I really don't think that matters in the game; I am sure that it is random.)
I have two other couples who are in the elder stage, they show the same, total of days with a day being added instead of taken way.
I don't remember how many days I have for each life stage, I have changed it several times.