
Well, you wouldn't believe what I read before this. This couple is not the MC couple they are side couple who is their employer cuz they are royalty.
The guy is 18 or 20 (I forgot, damn) years old and the girl who is his wife is 9 yeara old and they're happily in love
Tho I didn't focus much on them cuz MC's story is what I'm focus on.

Do you mean the queen and the king?
But They don't have a romantic relationship until she comes of age...
Political marriages were common in ancient times, even at very young ages, as royal families often used them to secure alliances and strengthen power, regardless of personal feelings or maturity.
So I personally don’t see a problem with young people marrying older partners in historical times, because life was very different back then. People had different responsibilities and expectations, and what might seem strange to us today was completely normal at that time.

bro- if they’re gonna play the historical card play it HARD. have serfs, have polygamy, bar women from career paths, refuse entry to people of color (not that this white washed manga would have any- but ya know). cherry picking historical accuracy is just giving a green card to grooming n lowkey pedophilia, why can’t she just be fucking older. it wouldn’t change the story much if at all. think of reading about their marriage in a history book “oh yeah this grown ass man married a child bc.. idk man star beasts n shit” he would get DRAGGED.

Except depending on the story, the others also occur. Usually it's the royal family who is allowed to have multiple wives (tho nobles still keep mistresses), there's mangas where it is looked down on for woman to have jobs, usually people of color (not exactly black. More like brown or tanned middle east ones) are called barbarians/savages. So on and so forth. There's nothing romantic between the two of them as of yet. Maybe in the future perhaps there will be, but nothing yet.
And it does change things if she was older. Imagine she was of marriageable age (assume 16 based on the times or even 18), then in the first life there's no need for ML to reject the marriage. The emperor intentionally chose a kid because he thought ML would reject the marriage which would give him an excuse to not give ML any rewards. At the same time, if FL was an adult, she would have been able to live alone and survive. Perhaps it would harder than now, but still doable if the author wanted it to be. So FL wouldn't have a reason to beg the ML to accept the marriage for her survival. So yes, things do change. It would lead to a different direction and could be another story at whole.
SHES A CHILD