Entre 5 e 6 1/2, mas mais perto de 6 1/2
Sua idade nunca é declarada diretamente, mas inferências podem ser feitas.
Han Tzu era um líder toon no Exército Drgaon sob Ender:
Han Tzu, commonly called Hot Soup, was the leader of D toon. He slid quickly along the lip of the star to where Ender knelt. "How about flipping off the north wall and kneeling on their faces?" (Ender's Game, chapter 11)
Os líderes de Toer de Ender eram veteranos de antemão:
His ragged little group of veterans, utterly without honor in their previous armies, were blossoming into capable leaders. So much so that instead of the usual four toons, he had created five, each with a toon leader and a second; every veteran had a position. (Ender's Game, chapter 11)
Seus veteranos eram todos mais jovens que Ender, com menos de 1 ano e meio na sala de batalha:
Not one of the veterans belonged to Ender's elite practice group. None had ever been a toon leader. None, in fact, was older than Ender himself, which meant that even his veterans didn't have more than eighteen months' experience. Some he didn't even recognize, they had made so little impression. (Ender's Game, chapter 10)
Ender tinha nove anos e meio na época:
Young as he is. we've never had a boy better prepared for command. Usually they go at eleven. but at nine and a half he's top flight." (Ender's Game, chapter 10)
E as pessoas (além de Ender) não foram promovidas até os oito anos:
Ender shook his head. It was the stupidest thing he could think of, to promote him now. Nobody got promoted before they were eight years old. (Ender's Game, chapter 7)
Isso coloca um limite superior em sua idade como sendo a idade de Ender (6 1/2 no início do livro), e um limite inferior de ser 8 no momento (5 no início do livro).
Como Praxis apontou, sabemos de Cheater que ele fez o teste da Escola de Batalha aos cinco anos:
We want you to be one of the best of all the five-year-old children in the world. (Cheater)
Mas não saber quando esta história é definida em relação ao Ender's Game faz com que seja de pouca utilidade.
Então eu colocaria sua idade como entre 5 e 6 1/2 quando o livro começar.