Board Thread:Naruto Discussions/@comment-26403664-20160228225013/@comment-7292165-20160417174855

Technically prime goes by ages in which you'd be able to reach the peek. Itachi was never passed his prime and in fact was just starting it. Even with the disease he could've been stronger than when he got it. For example, Part I Itachi apparently didn't have the disease, but Part II did, however, Itachi could've picked up on some new jutsu in Part II that makes him stronger even with the disease.