User blog comment:Sargenttacos115/Natsu and Gajeel age Theory/@comment-108.129.33.178-20140715134145/@comment-67.186.75.81-20140727114252

The different types of magic that exist in fairy tail are all probably older than 80 years so if it was based off of the age of the magic Erza and Happy shouldn't have been able to pass the barrier.