One of the things about The Sims 2 that is in many ways different from The Sims 3 is that individual sims can have their aging turned off. Or so this is what it seems. In the Sims 3, EA seems to have decided that it would be a nice idea if Ghosts (and soon Vampires) gave birth or fathered a Sim that is a Ghost (Or Vampire). In this case and scenario there is a problem. If the mechanics of The Sims 2 were to keep up, a ghost baby would never age so we come to EA allowed aging for Ghosts so at the very least Ghosts can have children.
But hold on here, isn't there a smarter choice? The Sims isn't an immersive experience. It's here for us to play around and entertain ourselves with the virtual people known as the Sims. So what if this was all for game balance? What if EA thought to themselves, "Having one sims would break game balance. The game would no longer be fun and then we would have complaints on how we need to fix this problem." This scenario is likely but maybe not what EA was thinking.
So here's another one, a scenario supported by the fact that there are no mods for individual aging to be turned off. EA simply couldn't program the ability to turn off an individual Sims aging. This idea and the first one I gave both seem likely. But I just thought of a simple fix if this were the case. have it so that every day a sim gains an extra day of life, much like eating life fruit for breakfast everyday. This would simply counter the aging and in a way a sim is made immortal.
Let's go back to paragraph one's idea shall we? What if Ghosts and Vampires age only because EA didn't think to have it so that when the babies were born we could choose when they stop aging or even further, make it so that they stop aging when they reach adult. And before you ask about mummies, assuming that individual aging were possible, EA may have just forgotten to implement it or they just thought it would break gameplay.
So let's look onto Vampires. EA could make Vampires one of the only life states that can attain immortality. If a vampire drinks plasma make it so that the vampires gain 2 days of life back. In this case a vampire would be able to avoid aging up for the most part.
Final words, I am aware that mummies have a longer life span and vampires will too but it just doesn't seem right that these supernatural life states have to die just because of whatever reason that one can pull out of the air. Be it because they didn't fully think through the whole having children part, EA didn't have the time to program it in, or they thought this would break gameplay. There are other problems I have with The Sims 3 but I overlook them because I could find mods to fix most of them. This I can't because it affects one of the things I originally liked to do in the Sims 2 and that was to have at least one Sim in a household become a vampire and have everyone else take care of him (WITH MONEY!).