For context, in Medieval Europe, until around the 17th century, it was common for noble girls to marry in their young teenage years to secure their political lineage, so it's not about pedo sexual fetishism like nowadays.
And, btw, the prince himself might be only around 16 years old. He's the same age as Yumie's brother and Monica, you know. They're not that far in age. And by definition, a pedophilia needs to be more than 5 years older.