These rules were put into effect starting with generation four.
One sim day – 0.66 years…below is what I calculated. I know people have already done this, but this is just what I calculated before I knew others had done it.
Baby – 3 days – 1-2 years old – about 2 years old when they enter next stage
Toddler – 7 days – 2- 5 years old – about 6 years old when they enter next stage
Child – 13 days – 6-15 years old – about 15 years old when they enter next stage
Teen – 13 days – 16 – 23 years old – about 23 years old when they enter next stage
Young Adult – 24 days – 24 – 40 years old – about 40 years old when they enter next stage
Adult – 24 days – 41 – 56 years old – about 56 years old when they enter next stage
Elder – 10 days – 56 – 65 years old – about 65 years old when they die
Aging is set to off once the heiress becomes a young adult.
Aging is turned back on once the heiress has her first child. This is so her parents will be able to be around for their grandchildren…since sim aging is weird and if you never paused aging, 9/10 sims would never meet their grandchildren.
That above method works because of this: Sims spend 36 days total in the baby, toddler, child, and teen life stages. If the first child is always born on the first day of the heiress’s young adult life, she has 24 days of young adulthood (which means she will be a young adult up until this child’s teen birthday) and 24 days of adulthood. Presuming the first child was a girl; and therfore, heiress, time would pause at her young adult birthday, leaving her mother still at 12 days of adulthood. When time ‘un-pauses’ because the next generation’s first child is born, that child’s grandmother has 22 days of life left in total, meaning she will be alive for this child’s life up until their teenage birthday.
The grandparents will be adults for the baby’s baby+toddler days and for one day of their child days before aging up to elder.
The grandparents might live long enough to see the child become a teen. Matters if they die on exactly the 10th day of adulthood.
Practically, anyone alive at the time of the heiress’s young adult birthday will live to see the next generation’s first child.
This lets me work on their story & life before having children without having to worry about aging.
If you need me to explain this better, just ask. It’s kind of complicated and I’m not sure if I worded it in an understandable way.