This has always bothered me, the fact that everyone's age is revealed except for Natsu. I kept thinking about it for a long a time and then remembered Zeref. Who stated that he knew about Natsu 400 years ago and how he knew that Natsu is supposed to kill him. The fact that Natsu's past has yet to be fully revealed (pre-Igneel) and the unknown identity of his parents enforce the idea that Natsu might have lived through Zeref's era. So could Natsu be actually 400+ years old as well? Could Mavis and Zeref be hiding something? Who were Natsu's parents?
What do you guys think? I'd love to hear your opinions and predictions :D