He might be able to play at some point, but he is so far behind in his development. Examples Manning threw over 900 attempts in HS.
He might eventually be able to play, but even if he gets a chance to start next season or the year after, I imagine we will be looking at a few years of growth as he gets more reps and keeps learning the position. This comes after years of sitting the bench in the NFL.
I actually don't think there is a comparable QB in NFL history that ended up being a good starter, but I sure hope I'm wrong.