The way I calculated it, Sims don't age at the same rate at all points in the life span. On normal life span, infants age about four months a day. Toddlers-Teens age about half a year per day. Young adults and up age a year per day. This means that they are 19 in human years when they become young adults. They are 43 when they become middle aged, and they are 67 when they become elders. Elders who don't have fitness bonuses die around the age of 77. Elders with fitness bonuses live longer, but I'm not sure by how much. Do any of you know?