My own theory is that PP is cursed in a way similar to that of Rumple. It is dark magic, power, and the search for eternal youth that have corrupted PP, but once he was simply a little boy who didn’t wish to grow up. In that scenario, it isn’t necessarily a person who corrupted PP but the search for power.
This is something I’ve been considering too. Rumple’s stuck at the age he was when he inherited the Dark One curse, so maybe Peter is stuck at the age he was when he inherited the Pan curse? PP does traditionally carry a dagger, doesn’t he?
As far as a 17 year old playing such a big, dark role convincingly, I admit, I originally thought they’d cast the role a bit older for that very reason. Have been meaning to see if I can get my hands on a copy of Robbie’s movie Ways To Live Forever, because judging by the clips of it on youtube, it was a serious dramatic role, (he plays a kid dying of leukemia), and he was pretty amazing in it. In the hands of a capable 17 year old actor like he seems to be, I do think PP could be portrayed in a suitably compelling way.
The other day Robbie tweeted that he was watching The Full Monty, which I figured was probably something of a research assignment to familiarise himself with how Robert acts, so he can know better how to interact with him on camera.