Avatar Kyoshi is widely regarded as one of the strongest incarnations of the Avatar. She was decisive in her role as the peacekeeper between the spirits and the four nations. As the Earth Bending Avatar, she was the predecessor to Avatar Roku, the founder of the Dai Li and the Kyoshi Warriors, and lived up to the age of 230 years.
At 230, Kyoshi was the most long-lived human that we have seen in the show. While earthbenders tend to have an unusually long lifespan in Avatar: The Last Airbender (such as Bumi still being one of the strongest Earthbenders at 112 years old), the novels might have revealed how Kyoshi might have unlocked the power to live for as long as she did.
Kyoshi learned about the secrets of immortality from Lao Ge
Lao Ge was a spiritually inclined assassin who ran with the Flying Opera Company, a gang of criminals that operated during the early tenure of Avatar Kyoshi. When it was revealed to the world that Avatar Kyoshi was indeed the Master of the Four Elements, she would join the Flying Opera Company and be taken as a disciple by Lao Ge.
Lao Ge usually disguised himself as a good-for-nothing drunkard but claimed that he was almost 4000 years old. This was never corroborated in the novels, or the show, only hinted at from time to time. The creators of the show have never confirmed this claim in any of the interviews.
There is a possibility that Lao Ge is a hundred percent legitimate, and Kyoshi would be the best testament to that, given she lived longer than an average human being. Kyoshi’s spiritual training, in part, came from Lao Ge, which was also the secret of his immortality.
If Kyoshi knew the secrets of immortality, what caused her to pass at 230?
The manner in which immortality works in the world of Avatar is through meditation. Lao Ge alleged that he ‘kept his body in order’ by meditation and keeping his body in alignment with the processes that it needed to keep going. Kyoshi could have learned this to extend her life till the age of 230. She is also rather youthful-looking compared to other Avatars who died of old age, This would point to the fact that Kyoshi probably had some juice left in the tank, but for whatever reason decided to give up immortality.
One section of the fandom speculates that it was all because of her attachment to Rangi, the Fire Nation noble who would become her friend, and later her companion. Kyoshi also had a slew of friends, who she would have to watch die as the time passed.
This could have led her to reevaluate her stance on immortality, eventually letting go of the need, sensing that she is only putting herself through pain by holding on to life. It is also possible that she realized that the power of immortality was not something she needed, given the Avatar spirit effectively renders each Avatar immortal (in a manner of speaking). She could have also decided to not outlive her daughter, and give up immortality to pass on peacefully.
