User blog comment:Sargenttacos115/Natsu and Gajeel age Theory/@comment-24.87.61.44-20121205064552/@comment-188.171.27.28-20130225183428

I guess they didn't even know which year they lived in until the dragons disappeared. Then they might have found out that it was year X777 when they got to the nearest human population and heard about the date.