User blog comment:Memnarc/Character Ages/@comment-7948498-20130907091743

Member ExcelCore seems to think that Nana and Momo are really 12 years old but are attending high school because if it was made explicit that they are that young, then Japanese censorship laws would put more restrictions on their fanservice scenes. That seems to be the only remote evidence he has presented in the history page so far.

Anyways, it's hard to completely determine the ages of these alien characters, especially if nobody knows exactly the growth speed, lifespan or calendar lengths of their people. Even Mea is considered to be Yami's little sister and yet they're both attending the same class. Their classmates are 14 years old, and yet those two could be anywhere from 12 to 24 years old.

For simplicity sake, it's just easy enough to conclude their ages based on their school grades and their appearances, and Nana and Momo look 14 enough to me.