I think that, because Leia is able to talk a little about how her mother behaved ("beautiful, kind but...sad"), it follows that Leia must have been a few years old before she was parted from Padme. The idea that Luke was taken away by Obi-Wan Kenobi to Uncle Owen & Aunt Beru straight after birth, while Leia stayed with Padme seems to me to have the most merit.

Perhaps Padme & Leia could have gone to Alderaan under Bail Organa's protection, meaning that Leia grew up with the Organa family, making them the most natural guardians once Padme was gone (however that may have occurred).

I suppose that, because Obi-Wan does use the words "twin sister" in ROTJ (after Yoda's death), one must conclude that Luke & Leia are the same age.

Good work on the actual ages, by the way!