Talk:Twilight Sparkle/@comment-24101825-20140708210740/@comment-24908786-20140709130210

The Journal of the Two Sisters specifically says that Alicorns age differently as Celestia and Luna were crowned Princesses and looking like they did in the show, but they didn't have their Cutie Marks yet.

As for Cadance and Twilight, there is still discussion about them, so I don't know. They were a Pegasus and Unicorn respectively before becoming Alicorns.