Agreed. From what I can understand it wasn't really his choice to have a fiancee half his age. Plus it was pretty common in history for these types of marriages so it isn't so weird. The fact that he is so respectful and is thinking somewhat about the difference is quite nice and very mature of him.
I mean really...for that other dude to be like "12 is more mature that you think" like eww...No, Maybe if the ML was 16 or whatever. But isn't he in his late 20s? And from the sound of things she has a lot less freedom in this than he does. Good on the writer for making the ML so sympathetic and even headed to consider the age difference like this. Otherwise I think it would turn everyone off but lolicons.
Yeah because of the terrible and odd nature of the political situation she was born into due to her parents, the crown prince was the only person she could marry, and in those times, you *had* to marry someone so there wasn't much choice for either of them.
Especially the Dude at the end of this chapter. He is really trying to just slowly build a relationship. He seems very aware of how odd it is that he is so much older than her. But he is being pushed to make their relationship a more romantic one.