There's a theory about the ghosts of Murder House and why some age, and why others do not. No definitive answer has been given by the production staff, the writers, the actors, or any ghost authorities. Calls to the Bureau for Paranormal Research and Defense have gone unanswered. But the crux of the matter seems to be that some think that if the bodies are still on property and not laid to rest that the ghosts will age.
We have seen one and only one ghost "age". She doesn't do it all the time, or to everyone, and she's already given an explanation of why. Granted that even the writers admitted that the explanation doesn't make a lot of sense. But we're talking about a one-off case. We can't begin to fathom what will become of Hayden, the only other ghost to whom this question may apply, because not enough time has passed.
Let me present an alternate theory that makes MUCH more sense: Becoming a ghost amplifies aspects of who you are, which the house manipulates to its own ends. Thaddeus became a hungry child. Charles became a single-minded butcher. Nora became a grieving ingénue. Chad's obsessive perfectionism and Patrick's libido rocketed well past what they had been while alive. Is it so hard to believe that in becoming a perpetual caretaker that this altered Moira's appearance? Hayden was never as starkly depicted as literally dark in coloring when she was alive. As for Moira's more vixen persona, that was clearly amplified as well.
Long story short, the "aging" theory has very little to give it merit. There's no way to prove it or disprove it unless we happen to hear more from the sources, and that's a long-shot at best.
So, looking forward to Season 2. Keep thinking!