User blog comment:Mamerge/What if Natsu is END? And Silver is Future Gray?/@comment-1177821-20140411033916/@comment-24956965-20140411054209

We have the same theories actually. :) Besides Natsu was shown unable to exit Freed's runes, those of which have rules stating that Persons over 80 yrs old cannot exit. Thus it is possible Natsu is 400+ yrs old...the same with Gajeel, though it is unknown for Wendy, who has her age confirmed. Just a theory though :)