The age of Zuko in the comics isn't fixed. It can change based on the timeline and events of each comic issue. Sometimes he might be around 22, and in other cases, a bit older.
To be honest, I don't have an exact figure. But you can look up on popular comic book databases or ask in comic book enthusiast communities to get a clear idea of how many The Legend of Korra comics are out there.
One great korra x zuko fanfic is 'The Fire and the Water'. It beautifully weaves their different personalities and abilities together. The story takes place in a post - war world where they have to work together to rebuild. Another is 'A New Alliance' which focuses on their growing friendship that slowly turns into something more. It has really interesting dialogue that makes you feel like you're right there with them.
The contrast between their characters. Korra is brash and bold, while Zuko has a more complex and brooding personality. When these two are paired in a fanfic, it creates a lot of interesting dynamics. Their different bending abilities also add to the allure. Fire and water, which are opposing elements, can represent their relationship in many ways.