User blog comment:Bato of the Heavy Iron Rock Hammer/Zeira dead or alive?/@comment-24546844-20140915013941

Well, in the anime Ano Hana Menma's ghost actually shows up as a teenagers despite having died as a ghost so following anime logic it's not like she can't really grow as a ghost.

If she's really a figment of Mavis imagination as I also believe then it's a way of Mavis actually not feeling lonelly. Think about it: if she actually believes Zeira to be alive but it's just her mind she would quickly notice how she is growing but Zeira isn't and that would cause conflict in her mind. So Zeira also growing up may be the way for her mind to adapt to Mavis own maturing process.

Have you watched the movie Cast Away starring Tom Hanks? To fight his own loneliness Chuck creates Wilson, which he, as the years go by start seeing as a true friend to the point of ignoring the fact that Wilson wasn't exactly a person. Maybe Mavis at the start knew Zeira was dead but her loneliness would make her mind create a projection of Zeira with whom she could be friend and as the years go by she would surpress the traumatic event of her death and start seeing the Zeira she created as real.