User blog comment:BlackWizardZeref/Fairy Tail: Chapter 380 Hell's Core/@comment-76.124.155.27-20140413200702/@comment-7418318-20140413204140

We saw a flashback of Mavis, Walrod, Precht and a 4th (definitely not Zeref) person, so that's a no-go for sure.

Also Fairy Tail was founded 105 years ago and thus not in a period in which Zeref would have done anything other than trying to stay the hell away from people so he wouldn't accidentally kill them.

And Natsu and Gajeel being over 80 (it was 80, not 100) is far from confirmed. There are plenty of ways to explain that away.