You can change jobs to a Mage in the Magic City, Geffen. Apply to a guildsman inside the Magic Academy, located in the 10 o'clock direction of the city. The Mage job change test is used to determine intelligence and memory ability through the making of a mixture in a particluar order. For detailed ingredient information, refer to the bookshelf next to the Mixing Machine. If you succeed in creating the mixture, you will be able to change jobs to a Mage. Requirements are Job Lv 10 or higher.