I am looking for the name of an 80's animated movie, possibly anime, in which a boy and a girl take a journey maybe to the edge of the world to find these special flowers that bloom and float up to the sky. If they catch them and hold on then they will never have to grow up. I remember at the end that somehow the girl doesn't catch the flower... or puff ball... or whatever and she becomes a woman. Does anyone know this movie?

Romeo and juliet style "The Sea Princess and the Fire Child" maybe