So, as we all know, Zuko is alive in Legend of Korra and that his daughter is alive and is Fire Lord. However, there are some quick facts I want to point out.
1. Most likely we will not be seeing her in Season 1
Currently, Republic City is in a civil war with Nonbenders fighting with Benders. There is no way Korra can leave just to see her. Zuko may show up to help calm things down as the creator of the city, but that is as far as we are getting in Season 1. However, in Season 2, that is a totally new ball game with new villians and the likes, so we may see her then.
Obviously, his daughter is going to be old. Think about it.
Zuko was 17 at the end of ATLA and as he was in a relationship, (Suko fans, it is still Maiko at the moment), he was most likely 20-25 when he was married. Keep in mind, it is a duty for heirs to be born so obviously his daughter was born early in the marriage. 1-2 years later at the least. That would make her around 50- 60. If Fire Nation Royalty does show up, it'll most likely be his grandchild or great-grandchild.
That's really all have to go on at this point. Feel free to mention anything else and I'll add it.