[The fussiness about age gets a very tiny smile out of him, but he makes sure it's gone by the time Yuu ever looks at him again. When he was sixteen, he didn't think he was young either.]

It explains the recklessness. [Sasuke is such a chill dude to be told all of this. Thanks, fantasy ninja Japan.] The loser I told you about, the one who wouldn't let me become a monster.

He has something like a demon inside of him, too. A Tailed Beast.