Well it depends on what you mean by young.
he was around 16 when he did kill his borther(in naruto shipudden)
Itachi let Sasuke kill him or he could have killed sasuke
actually, sasuke didn't kill itachi. when they fought itachi was hurt or sick, and he died. he never intended on killing sasuke. sasuke didn't know about itachi's past
naruto doesnt kill itachi, sasuke does. Nor does Sasuke. Itachi was already dying until the battle with Sasuke. I think he had TBC.
There is no "they"...only Sasuke kills Itachi. And, no, Sasuke is not friends with Naruto.
For revenge
No.
kirin justu
naruto want to kill him
Yes
No, they did not. Itachi died fighting Sasuke. Naruto and Kakashi were trying to find Sasuke at the time.
no SASUKE killed orchimaru.
Yes, he did in Shippuden.