The LOST Boy

I just wanted to make a quick post on the mysterious boy who has appeared twice in the jungle.  First we saw him in Episode 4 (The Substitue).  He had blood on his hands, appeared to Flocke and said "You know the rules, you can't kill him", possibly referring to Sawyer.  Sawyer could also see him, but Richard couldn't.  This is what he looked like:

Here's another close up:

Now this mysterious boy appeared again in Episode 12 (Everybody Loves Hugo).  But he was older looking, and had darker hair.  He didn't say anything, but he smiled at Desmond.  Both Desmond and Flocke could see him.  Here's what he looked like in Episode 12:

Same boy, same actor, but why does he look so much older?  Why does he have dark hair?  And who the heck is he?  I thought he was Aaron earlier, but now I'm not so sure.  Any ideas?

Here's what the casting call for this character said:

Guest character: TEENAGE BOY - Caucasian, 12-14. Dirty blond hair. Wise beyond his years. He's got intense, searching eyes. He's dealt with a horrible family accident. Even at a young age, he has been put in charge of something very important, and it weighs heavily on his shoulders. RECURRING GUEST STAR.

Horrible family accident...

Add this to the list of mysteries!