Shortly after the Kyuubi was sealed into Naruto, the council decided what they should do with him. Danzo suggested that he be turned into a living weapon. Sarutobi decided to accept Danzo's proposal and Naruto was trained to be Konoha's living weapon. When he was six, Naruto became a member of ANBU Root. Now, at age 12, he is an ANBU Root Captain while the others his age like Sasuke Uchiha have just become Genin.