The retainer is granted to you once you complete one of the main quests in Western The.
I got good advice, and it was to follow all the 'flame' quests (quests where the npc had a flame around it. So, I put off doing leve quests, duty and followed the flame quests.
I got the retainer at level 22/23. Just in time, to run out of inventory and armor inventory space.
Advice to self: Don't level all the jobs and classes, cause you just don't have the space for it.