He's 14". Sorry to here that your Piranha is like that. But to be honest most P's are that way.
This guy isn't aggressive toward people like a 4" I have, but when he eats you could appreciate that he would easily clean of 2 or 3 fingers in one bite. So I am happy he is not a finger chaser like my little guy.
Stick with cichlids and you won't be disappointed.