Aang’s backstory in Avatar: The Last Airbender went through some changes when the show was being developed, including aging him up slightly.
Aang’s backstory and character development went through numerous changes before Avatar: The Last Airbender premiered. Aang’s journey as the Avatar is rather unique compared to his predecessors as well as his successor, Korra. Instead of being formally trained in bending all four elements during his teenage years, Aang was notified about being the Avatar and then was subsequently given all the responsibilities associated with the birthright when he was just 12 years old.
It was too much for him to handle at the time – understandably so – and he fled the Southern Air Temple, ultimately finding himself being trapped inside an iceberg near the Southern Water Tribe. Up until he found out who he truly was, Aang was a kid who wanted nothing more than to play with his friends and airbend – but the world had a different path for him to follow. What’s interesting is that, while Aang’s story remained largely the same in the final version of Avatar: The Last Airbender, his backstory was changed from the original concept.
According to series creators Michael Dante DiMartino and Bryan Konietzko in Avatar: The Last Airbender – The Art of the Animated Series book, Aang didn’t just hibernate in the iceberg for a hundred years, he would’ve been in there – or somewhere else biding his time – for a thousand years. He would’ve also been the last survivor of an ancient, technologically advanced nation, which, at the time, played into his clothing being futuristic and his staff having a more metallic look. Of course, things changed and DiMartino and Konietzko tweaked Aang’s story to be more believable in the world of Avatar.
Despite the changes to Aang’s backstory, the fundamental parts of his origin carried into the main series. Aang was still the last survivor of a civilization (the Air Nomads) and he did come from a peaceful time, now finding himself caught in a war-torn world (the Hundred Year War, which began right when Aang disappeared). Furthermore, Aang’s staff, his pet monkey Momo, and his flying bison all found their way into Avatar: The Last Airbender’s story.
It was only after DiMartino and Konietzko settled on the concept of the four nations being comprised of elemental benders that they decided to make Aang an Air Nomad. They also imbued him with Tibetan and Buddhist philosophies, which is why he always believed in non-violence. “He was capable of taking down anyone in his way, but because of his nonviolent upbringing with the monks, he was hesitant to fight or hurt others.” That line became the cornerstone of Aang’s characterization, which followed him up until the series finale when he defeated Fire Lord Ozai.