Responses

the marriage age in ancient settings can even be as low as thirteen (i have read many mangas with such a setting) , the guy is just doing this to keep her to his royal family but is also protecting her from her trash family that will try to take her back by force and when her growth spurt is completed she won't look so under aged any more
Doesn’t matter if her mental age is something like- 33, she’s still 15 physically. I’m gonna pass because of the age-gap.