Just wondering, because I am level 26 and have completed the Companions, Civil War, Meridia's Beacon, Vanilla Main Quest, Dawnguard Main Quest, and will soon work on the Dragonborn Main Quest. I feel like level 26 doesn't correspond with the amount of quests I have done. I normally play Adept unless I am in a tough situation, where I turn it down to Apprentice or Novice (but I always move it right back up to Adept afterwards).
Here are the Questlines, if you're unsure of the ones I was talking about:
-Any Guild (Companions, Thieves, Brotherhood, College)
-Civil War (Imperial of Stormcloak)
-Any Deadric Quests
-Any Major Questlines (Main Quest, Dawnguard, Dragonborn)