User blog comment:FairyRaven/Fairy Tail Chapter 448: Fight the Power! Review and Commentary/@comment-114.79.32.226-20150817072920/@comment-7418318-20150818073904

Well... Mavis did actually age. While her appearance didn't change from the 12 year old look, her body itself did age and she would eventually have succumed to old age, if her life hadn't been cut short.

So if that body is still alive inside the crystal and doesn't die from being set free, she should theoretically age and have a limited lifetime.