I think there's good reason to believe that Amon is Bumi, Aangs son. First, I have to agree that being the one nonbending child of the Avatar would majorly suck. Also, I think Amon moves like an airbender, and I wouldn't be surprised if the "my parents were killed by a bender" story is a lie. Here's my theory: Amon/Bumi learned to fight, but not bend, from his father, and from hearing all his stories and talking to his friends, learned about chiblocking and how his father took Ozai's bending away. I'm also thinking that Bumi maybe met up with Ozais spirit along the way. Bumi invented a modified form of chiblocking that permanently inhibits bending, although I also suspect that another energybender could undo it. I think, if anything, Tarlok is in Amon's pocket, but he's not the man behind the mask. He's definitely helping Amon in secret, but probably just because of some cockamamie story that Amon will leave him with his bending, and the idea of being the only remaining bender in the world would appeal to Tarloks need lust for power.

Besides, Tenzin has never mentioned his siblings. He has had no reason to. Watch Amon fight. He never strikes, he always just slides out of the way until he gets close enough to chiblock. He fights like he was trained by an Airbender.

Ok here it is guys, I dont think we can rule out Amon being the Avatar that lost out the race to Korra(he coulda been born like a few seconds after her or sumn idk) but if you think about it then it could make sense because Aang almost messed up the cycle when he got put on the verge of death while in the avatar state...The thing i was thinking was that he could've been an earth bender who was chosen in the cycle(which in itself would explain his entire backstory seeing as the fire nation occupied Earth cities and most of them had farms) and are u really going to eliminate that story because "Amon is older than Korra"? think about it the only thing u know about him is his voice and apart from changing it can u really say only old guys have deep voices?

Ignoring that theory i'm more on the side of it being Bumi(aang's son,allot of people say it's not(You're just guessing as we are) it makes more sense of it being him than any other story so far....Look at thing, we all know the backstory is most likely fake and Amon just came up with it to gain support(so that by itself eliminated all debates of how it couldn't be him), another thing is that people say "It can't be him because only the Avatar can manipulate energy" FALSE, the Lion-turtle did in fact tell Aang that before the time of the avatar people could bend energy and Aang was just the first to learn it after a long time. it makes sense that Aang would teach it to him so he'd have protection and he could've learned Chi blocking on his travels and his motive would be justified (being the only child of the Avatar that can't bend i'd be pissed too)..So that's a near perfect Theory as to who he could be