At the time of the battle, Sasuke was 16 years old and that's the time when he killed Itachi. Sasuke trained with Orochimaru on a considerable level in order to become worthy of battling it out ...

As a child, Sasuke's idol was his older brother. As a child prodigy, Itachi rarely spent time with his family, leaving Sasuke with a void in place of brotherly love and mentorship.