Which is it it's majour draw back, the story telling needs to mature and not just in the way that something like Devil man cry baby matured. It needs to be aged up, if even it was to the university level it'd allow for much broader character story arcs and dialouge but nothing else has to change in the style of the game. Why does it always have to be teenagers, look at steins gate, they managed to make the perfect anime with adults.
I mean, aging up characters in this one wouldn't mean much, seems to be following similar bits to Nocturne, which would be a post apocalyptic world for most of the game.
The core of the writing of Shin Megami is about ideals, a side of chaos, law and the like, not about character arcs per say, the main characters you'll interact with will be about those ideals, making them adults won't really make a difference here.