Re: Neighborhood Stories off yet unplayed Sims are still aging and having kids.
Aging is a separate setting from neighborhood stories. You can turn aging on or off for played and for unplayed sims.
They’ll never just be frozen if you’re playing in the same save though. Pregnancies will progress, university semesters will progress, and when you go back to the household they will be doing something different from where you left them. If you want to stop playing a household for a while and then come back to find them exactly as you left them, then you should play in a different save until you come back to them.