What I do is only make over townies who are important to my story of gameplay. I also go in and delete random generated townies about once every real world week. I place my own townies who have needed skills for the jobs in-game. I don't remember where I saw it, but I googled for how many different types of townies the game wants to generate to fill roles. All you need to do is create those townies, place them on a lot and evict them to be "not in world." You then mark them as unplayed and put them in other households part of mange worlds.
While the game might still create random townies, it lessens the amount generated. My oldest same is 30+ generations. Another thing to do is only age played households and select onky the households you interact with frequently to by played for aging.
