Board Thread:Theories and Speculation/@comment-1872728-20200725151448/@comment-46279039-20200729225746

Yes, we know he did the training but he didn't have a suitable body. I assumes it was also the fault of the arms. Anime suggests that he was in bad health and the body in which he was in possession rejected him, showing him coughing, as after the clash with Hiruzen.

He knows something, but cannot use a Sage Mode and therefore not even Senjutsu.