Wow someone really read the novels o.o; almost refreshing question looool.
I believe started in college? Correct me if I’m wrong. (I guess I can stop being lazy and go read that book, it’s right next to my computer x.x;; all the drrr books are forever next to my computer to answer these questions lol), (Ok i was lazy, i used durarara wiki and yeah it started in college).
It depends on what you consider is power. I only translated Narita’s twitter, I’m really not Narita so I won’t probably question his words. But I’m guessing ‘power’ means how much ‘destructive power’ you have at your possession. So Aoba probably could use his cunning skills and multiply it with his friends to cause havoc… while middle school Izaya could have manipulated all the humans in gambling ring + his classmates + anyone he feels like in general, to cause similar destructive power….
The difference is that Aoba relies mostly on his Blue Squares because he knows and can predict them. And they obey him. He doesn’t really reach out to other people. He prefers control that way. (Even using his older brother, which he believed he had more control over). But Izaya is more confident in his skills to understand and manipulate ALL humans, so he doesn’t seem to have that limitation that Aoba has? Izaya doesn’t keep friends. He doesn’t feel the need to. Aoba however, does.
… is my guess lol. Again, I’m not Narita, so technically I probably shouldn’t be answering this question lol.