depends on the mage
Actually it depends on the game
- The orignal Final Fantasy can be selected at a new game with a Red Mage
- Final Fantasy III's Red Mage is obtained after you find the first crystal
- Final Fantasy V's Red Mage is obtained after you found the first crystal
- Final Fantasy XI's can start the game as a Red Mage
Final Fantasy XII I'm not entirely sure on how you get it, but I think you were just about the job class Red mage.
- Hope this was helpful