Done because I can. (Though I don't own Avatar.) And because nobody looks at this kind of stuff enough.
Sokka is always a little surprised to remember that, once upon a time, he had been skeptic of Aang. Sometimes, he still is skeptic of the monk - shaved again now, bald as a newborn babe.
Still scrawny and a vegan, too. A little taller, the blue tattoos still in place, his ears still big. (But smaller, Katara is fond of teasing, than his own.)
And when Aang does something extraordinary - blows a tornado out of existence, calls up a breeze with a flick of wrist - and the other non-benders are amazed, Sokka has to re-realize that that isn't normal, however used to it he is.
Because that scrawny kid who loves to go penguin sliding almost as much as Sokka's little sister is the Avatar.
The newly instated Southern Water Tribe Chieftain shakes his head - half amused, half exasperated - as he realizes his best friend is a legend. One he'd grown up hearing stories about. One that people praise as a savior, cursed as a coward or heretic, and look to for hope. Hope of what is their own choosing, but Sokka knows the truth.
Aang is the Avatar and still a kid, for all of his power.
So Sokka contents himself with just hoping that he catches some fish that day.