Gabriel had doubted that Balthazar and Castiel would be suitable flying partners, since Balthazar's first instinct was to dive head-first off a cloud and Castiel pretty much had to be pushed off, but he needn't have worried; both were natural born flyers and could still be seen playing together long after the stars had come out...
I'm not trying to break your heart, honest... but they were friends once, right?
Request for ~DestielandCrowley
EDIT: Somebody sent me a link to a vid of Misha and Sebastian talking about how Cas and Balthy met during flying lessons: [link]
Love it! Supernatural (c) CW