In an effort to clarify many of the new Sims 4 features revealed during our E3 interview, SimGuruGraham goes into more detail about aging over at Mod The Sims.
Let me help explain aging options a bit more clearly.
First, you can globally set the lifespans of Sims to be short, normal, or long. This applies to all Sims, no matter if you’ve played them or not. Second, you can choose if unplayed Sims (any Sim that you’ve never taken control over) automatically ages or not.
Third, for Sim families you have played as (for rotational gameplay), you can enable or disable automatic aging and it will apply that setting to all of those families simultaneously. You do also have a third choice for played households to set it so that only the family you’re currently playing automatically ages, and all your other played households will pause their aging until you’re currently playing them again.
Further, in Live Mode, you can use a birthday cake to age up not only your own Sims, but you can use it to age up other unplayed Sims without having to play them, at the time of your choosing.
Someday I would love to expand the aging options so that they can be set per household, but we’re already shipping robust options in the base game that give you a variety of approaches to how you play.