It's after a level 17 quest. It's the "final" quest in the first chain with the walking sands people.
The walking sands girl/leader will say, "As a reward we are giving you a retainer go talk to XYZ in ABC place."
It took me forever to figure out. I don't know why it's not more prominently noted on the internet. I wish I could remember the name of the quest. I think it's this one, http://ffxiv.gamerescape.com/wiki/The_Scions_of_the_Seventh_Dawn
But that might be the first in the 17 chain.
It's after you do three dungeons.