User blog comment:FairyRaven/Fairy Tail Chapter 325: Unity, Review and Commentary/@comment-49.176.34.54-20130330054337/@comment-7418318-20130330072815

We still don't know what exactly was up with the 80+ barrier.

For all we know the Dragon Slayers could really be only their apperent age (plus the 7 year timeskip for FT's three DS), which means 12/19 for the yougster Wendy. So Hisui could easily be old enough to be one and still have the King as her real father.

But why would anyone believe that she's a Dragon Slayer in the first place? I don't remember anything that even hints in that direction...