There are 8 main Magi levels. You start out with the rank of Apprentice Magi. After earning your first rune, you are promoted to the rank of Junior Magi. After earning 3 (?) more runes and 1000 (?) XP, you will then reach Magi status. Those requirements are then doubled (?) for the rank of Senior Magi. Complete the final few runes and both parts of the Master Magi quest. In return, you will be rewarded with the lofty rank of Master Magi!
Levels of Magi are quite useful. You can be able to keep track of how good of a Magi you are. So, let me name all of them individually. There's Apprentice Magi, Junior Magi, Magi, Senior Magi, Master Magi 1-16.
There is a (unofficial) rank known as Heroic Master Magi. Most people will define this as any Magi who has completed all the Master Magi and Heroic Quests. As well, there are additional Master Magi ranks (Mstr Magi 2-16) that are merely titles. Master Magi 2 can be achieved by earning 3000 more XP from repeating quests or doing adventures. For 3-9, you add another 1000 XP to the requirement for each level. So, Master Magi 3 will require 4000 XP starting from zero. For 10-16, the requirement doubles each time. So, for Master Magi 10, you will need 20000 XP (starting from zero, doubled from Mstr Magi 9), and your final requirement for 16 is 200,000 XP.