i just read a theory that aang knew about harmonic convergence and that he would be too old to stand a chance against vaatu when it came, and also if he died a short time before it the next avatar would be too young to stand a chance so he waited as long as he could before killing himself so the next avatar would be at peak age and physical condition for harmonic convergence
So I found a thing…
"Since the very first episode - Korra’s entire self-identity has revolved around her role as the Avatar.
She grew up isolated from her own culture, kept in a White Lotus compound being told by everyone that being the Avatar and keeping balance in the world was her sole reason for existing.
Every major threat she has encountered so far has been a threat to that identity. Amon threatened to take away her bending and her ability to act as Avatar, Unalaq/Vaatu succeeded in destroying Korra’s connection to her past lives, and Zaheer nearly succeeded in destroying the Avatar cycle.
All these conflicts, Zaheer especially, have left Korra wondering whether the world really needs, or wants, an Avatar anymore. It’s caused her to question her entire reason for existing.
Now here she is - crippled, broken, traumatized, not knowing whether she’ll ever be able to fight again, questioning her entire reason for existing, and here comes her respected mentor coming in and telling her 'Don't worry, my people will maintain peace and balance, we don't need you to do anything except feel better.'
Which only succeeded in confirming her deepest fears.”
so maybe in book 4, korra goes on a life changing field trip with zuko to find out who she really is other than just the avatar?