Board Thread:Versus Debates/@comment-3523655-20191213031023/@comment-9782468-20191213200356

It showed him training with it as a kid, it didn't show him successfully using it in combat. Since he never mastered it, he may have excluded it from his repertoire until the increasing threat of the Akatsuki forced him to train to use it in battle.

In any case, I said if we go by abilities shown in Part 1. Keyword is shown. Because it's hard to speculate when we give Part 2 abilities to Part 1 characters. For example, Kakashi unlocked his Mangekyo when he was around 14. Yet he fought many difficult opponents and his Hokage even died without him ever showing the technique in Part 1. So usually if we say Part 1 Kakashi, we exclude Kamui, despite knowing he unlocked it.