So, I was talking with some of my brony friends IRL yesterday, and we brought up the point of how Luna looks totally different in her Season 2 and 3 appearances than she does than she does in the second half of the first episode. Some might argue that this is because of improved budget and skills at animating the ponies. I disagree.

Now, unless you've had your head stuck in a hole for the past two seasons, you know that instead of looking like this...

Luna now looks like this...

Now, some people would say that this is all because of the improvement in the budget and the animators, and that this was done for the sole purpose of making Luna look more... Princessy, but I disagree.

Luna was banished to the moon for a thousand years. And she wasn't banished in the form of herself. She was banished in the form of Nightmare Moon, which suggests that the regular Luna might not have actually aged in those thousand years, which Celestia certainly did. The Luna we saw at the end of Friendship is Magic, P2, was the Luna from a thousand years ago, the way she looked like before actually becoming Nightmare Moon. Celestia undoubtedly looked similar a thousand years ago - it takes a while to transform into a flowy-maned goddess. That much must be true, considering that Cadence and Twilight are princesses of this millenium, and still have normal-looking manes. Surely, Celestia must have once been like that, too.

Luna, looking like she did a thousand years ago, was helped along by modern, millennial Celestia to restore her original form, suppressed by Nightmare Moon, to its proper age with the use of an age spell, which is a spell that can only be performed by the highest-leveled unicorns.

Of course, there's always the question of whether age affects Alicorns as it does everypony else. I think it does, but that since alicorns are powerful magic users, they are able to maintain their youth, but doing so over extended periods of time changes their figure to the more powerful, leaner, taller form an alicorn has, in comparison to others. Perhaps they still mature under the age spell, and all the spell does is prevent them from whithering away. Who can say? A lot of this is speculation. But I'm getting off topic.

That's my theory of how Luna matured so quickly. Maybe one day, in this upcoming season, we'll see more of both princesses, and get their stories. How they became princesses, maybe?