I turn aging off when I go play with the other households. I only keep aging active when playing with the heir to my legacy and play for one sim week then check up on the others. With aging off on the others I can set them up how I want and let their families grow as needed. Just have to monitor when their aging progress so I'm not missing out on any important life events for them; birthdays and death. It can get time consuming but I love each of my families and they're all different in some way. But playing like this does take a long time to build up generations, the furthest i've gotten is 5 and I wanna go for 10.
@MVWdeZT has a good idea turning on aging for the played household only. I haven't played like that but it isn't a bad idea if you wanna keep the premade families from getting old and dying off since there isn't story progression in the game.