Ender in Exile — Orson Scott Card

At the close of Ender's Game, Ender Wiggin knows that he cannot live on Earth. He has become far more than just a boy who won a game: He is the Savior of Earth, a hero, a military genius whose allegiance is sought by every nation of the newly shattered Earth Hegemony.

He is offered the choice of living as a pawn -- or he can join the colony ships and go out to settle one of the new worlds won in the war.

Ender chooses the stars. With his sister, Valentine, they take passage aboard a fast ship to Colony One. The voyage will take two subjective years, while forty years pass on Earth and at their destination... and when Ender arrives, he will become governor of the new world. Meanwhile, he is under the command of the ship's captain: a man with ambitions, a man who finds it unthinkable that he would be ruled by a twelve-year-old boy. Admiral Morgan doesn't understand what Ender Wiggin is. But he will.