Imagine the sims are coming out with a massive update

"Mr_MuffinTop;c-18177204" wrote:
Improvement to the Neighborhood stories that works more like MCCC so I can flag sim families as immortal, stop the aging of certain families while still allowing them to have babies.

We already have this. If you have the baby toggle on in the EA story progression, they will have babies whether or not aging is on. Also we can decide which households age and which don't:

Suppose you want aging on to be the default but you want to select specific families to not age. In the game play options, having aging turned on for unplayed households. For played households, set aging to active household only. This means that played households other than the one you are currently playing will not age. If you want a household that you've never played with to stop ageing, you load into the household briefly so that it becomes classified as a played household. If you want a household you've previously played with to start aging, just switch them to unplayed in the manage household feature.