@canelacaliente I've seen some of this too. But I've found is that it seems to self correct depending on what you are doing in the game. What appears to happen in my game is that the game creates the npcs it needs for certain things like stall venders and they are typically all adults. But if you go to one of the parks, you'll see npc kids and maybe a few teens there. Check manage households and you'll find that new npcs were created that have either a single parent and that child or teen you saw or both parents and the child and or teen. If you go to a bar, the npc bartender can be any age from YA to Elder. Same goes for ghosts created when you have a lot with the haunted trait. Those are examples that I've seen in my game. Now I travel a lot with my playables so I get a ton of npcs created especially in some of the game pack locations like the Realm, Strangerville and Salvadoria. But also at the CL festivals and even just going to a park. So I've concluded that most of the not in world npcs are created for a specific purpose and the game doesn't create them unless it needs them. If all you are getting is adults, then you're probably not doing much travel to the locations where the game needs to create the npcs you no longer see in your manage households.
I've definitely noticed this while playing in StrangerVille. Almost all townie households spawned for StrangerVille are single-Sim adult households, with the occasional single-Sim elder household peppered in. Very rarely do I see any young adults.
Strangerville generates a lot of single Sim households, because it has roles unique to just that world: like the infected Sims, military, conspiracy theorists, and scientists that are all needed to complete the story. I will say it starts to seem excessive after awhile, but it's been that way since the pack was released.
