" You certainly must be very old to have reached the ground already." "Oh no," said Milo seriously. "In my family we all start on the ground and grow up, and we never know how far until we actually get there." "What a silly system." The boy laughed. "Then your head keeps changing its height and you always see things in a different way? Why, when you're fifteen things won't look at all the way they did when you were ten, and at twenty everything will change again. "