User blog comment:FairyRaven/Fairy Tail Chapter 424: Avatar, Review and Commentary/@comment-4700320-20150317190122/@comment-25111584-20150317190708

Actually, Gray is around 8 years old (according to the wiki's timeline anyway) during IT, so Mary wouldn't be much younger to him during IT. Currently, she'd actually have to be older than Gray by quite a few years because of the 7 year timeskip. So, actually, this Mary looks to young. But, then, Ultear also didn't change much during those 7 years, so can't say much about going by appearances. :P