User blog comment:IamJakuhoRaikoben/Chapter 357: The Nine Demon Gates, Review./@comment-4449950-20131025123936/@comment-7418318-20131025124927

That guy not Tempest. That gives me an idea: It'd be cool if Laxus and the raijinshuu would have a very hard fight and manage to defeat that guy.

As he lies beaten on the ground, another Demon comes in. The Lion-thing calling it "Master Tempesta", begging for forgivness and mercy, but tempoesta just finishes him off and then wipes the floor with Laxus, before strolling off again.

Regarding theory 2: Maybe Zeref cast the same spell on Mavis that prevented himself from aging, but the spell couldn't stop Mavis from being killed and that's why she remained in the body of a child, but has the wisdom of someone who lived a long time (because she did).