A flexible, modded aging manager is required to allow aging on (or off) at the individual sim level or on a subset of sims. The usual choices are
NRaas StoryProgression or, if SP is not viable for some reason or the player does not really want the rest of its features, then
Buzzler's Aging Manager (the two really shouldn't be used together, though).
If using NRaas SP, then it becomes NRaas > SP > ...
Sim Options > Death: Allow Aging > T/F (on an individual sim if this is what was wanted)
Caste Options > Teenagers > Death: Allow Aging > T/F (on City Hall or an in-game computer for a class of sims if this is what was wanted)
Town Options > Death: Allow Aging > T/F (on City Hall/computer for the rest of the town)
Sim Options will trump the others, Caste Options will trump Town Options.
