[action]
It's not age so much... Though I have heard some people tease her for still having hers at that age. [Physically, yes, Shinonome-sensei can be considered a grown-up, but the concept is very different from being an adult.]
It's doing adult things that make you lose your ears. [Ritsuka blushes faintly as he says this - please don't make him spell it out, Charles. Because now he's thinking of Soubi and all the other adults he knows, and it's embarrassing and a bit painful to do so.]