User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-27029561-20151207182136/@comment-9595671-20151207195817

Some could say that the Dragons were involved, and for Natsu the whole END thing was another layer.

I personally think both could have been reasons, but more so the dragons cause the story kinda implies they went into the future with their children and then went inside of them, it's not said if Freed's runes work on only physical age or not.

It also explains why no one knew about Dragons till Acnologia, essentially they died out 4 centuries ago, and the surviving dragons were hidden which gave no evidence to their existence minus their kids.