Some facts about Genius Itachi Uchiha the pseudo-MC of the series

Born with a tumor

At the age of 3 found Ryo and gotten attached to him

At the age of 5 witnessed war and becomes a pacifist and contract crows as his summons

At the age of 6 joins the academy and graduate in a mere 11 months (that's an unbeatable record)

At the age of 7 graduates and already thinks like a Hokage

At the age of 8 completely mastered Sharingan (again did in 1 year once again an unbeatable record)

At the age of 11 Becomes Jonin and join ANBU Black Ops (In 3 years from genin to jonin once again an unbeatable record)

At the age of 13 become the ANBU Captain

At the age of 13 massacres entire Uchiha clan and saves the lives of the countless innocents

At the age of 13 joins Akatsuki

At the age of 18 powerful enough to fight Kyuubi and sage head to head

The tumor spread too much he could not use more than 60% of his true strength

At the age of 21 died for Sasuke

If he lived more than just 30, he would have surpassed Madara and Hashirama