From what I remember:
There was scene where two characters are on a flying ship in the air, and staring out into the sky. I also remember something about reverse aging and the girl's hair turning white to brown for some reason so that she could be with the other character.
It's an animation film and I'm 70% sure it wasn't made in the 2000's. Or it could be, but I remember it being an old movie.
It also didn't seem like an American or British animation, probably Korean. But it was in English, so please help. It's bothering me so much!