The visual of Mina paired with someone who appears inappropriately old may be disconcerting, but at the heart of this anime is a beautiful love story about a promise made by a boy, to the person ruling his heart. The way love is discussed is extremely mature, and with the exception of one or two moments, Mina didn't act like she looked. She acted like her real age.
I also really appreciated how multifaceted Mina is as a character. She didn't shy away from the darker side of statesmanship and you could really see the struggle between her idealism and realism. She was incredibly multidimensional and is worthy of playing the main protagonist. I loved it and wish there was more quality writing like this in other anime.
Seriously.If people freak out about this, why aren't they freaking out about all of the cherubs that appear constantly on old English/romantic/too-lazy-to-remember art? And don't forget! those anatomically correct naked children appear in elementary school text books! The horror!
*facepalm* -sorry, slightly annoying since the only thing that seems to be constant in our culture is hypocrisy.