Townie Aging Question

This is the first time I've turned on townie aging in TS4, and I'm a little confused - how long do they take to age? It seems like hardly any of my townies are aging, and the first born child is now a teen, so some of the younger generation should be about there too. Do they go off what you have your lifespan set at, mine's custom, or do they have their own aging process? Would be nice to see Elsa et al grow up already!