User blog comment:Monét/Who is better, Erza or Mirajane?/@comment-3995030-20121219060001/@comment-4924995-20121222141852

Erza passed the S-Class Mage test first. She was and still is the youngest mage to become an S-Class Mage. She was only 15. Mirajane became an S-Class Mage a year later, when both she and Erza were 16 (Mirajane and Erza are the same age)