Board Thread:General Discussion/@comment-4913740-20130628164607/@comment-4913740-20130701074132

Apart from the possibility of retcons, people can look older or younger than they really are. For example, I myself am 18 but I look quite younger.

And also, height is no indication either. I have a friend who is the same age as me but considerably shorter. Including that I am considerably taller than most of my friends as well, it's entirely possible this is teenage Mantis who is just a tiny bit shorter than average.