So many theories right now. Some say Zuko is the main baddy. Also, am I the only one who finds the steampunk anti-benders loving awesome? They have like, electrified batons and wires n' stuff. It's cool.
first off- zuko is probably around 98 years old ATM
if he was actually Amon, he probably would've been breaking his back every twenty seconds
secondly, Zuko loved bending. some might hypothesize, more logically, that Amon is Sokka's son, considering Sokka was a non-bender and was very jealous of the rest of his crew, as well as feeling pathetic and useless. This can easily turn into animosity, which could easily be taught to a child, not different from how the Westboro Baptist Church brainwashes their children.