In my game:
Infant 0-1
Toddler 2-5
Child 6-12
Teen 13-19
Young Adult - 20- 40
Adult 41-65
Elder - what's left (lol)
I have custom age settings through the MC Command mod, so one thing that's perhaps a big departure from a regular game, is that I have adults set as past child bearing age, well for the women. I only have women who are newly aged up to adult able to get pregnant, obviously, for men there is not a restriction.
This way my sims can be grandparents as adults and really be around for the grandchildren to grow up and start having kids of their own before they pass away.