Board Thread:Theories and Speculation/@comment-1872728-20200725151448/@comment-32685487-20200725191630

After going over all of that. Oro is a sage because he can mould and use Senjutsu, he is NOT a "perfect sage" because he can't stay in Sage Mode because his host bodies are too weak for it. Hence him using his Sage abilities to create the Curse Marks with his very own Senjutsu.