Medieval people don't really give a rat's ass about present day standards.
People in those days live an average of 30 years.
Either you marry young and procreate or risk the extinction of your whole clan. Their children even have a 50-50 chance of living considering how unhygienic those days were.
That's the reality, and I commend the author for doing his/her research
In Scotland you can marry at 16 with your guardians permission. But yeah, a 12 year gap when your so young is kinda big, but I think age difference matters less as you get older, lol you probably wouldn’t care if they were 60 and 72 right ε=ε=(ノ≧∇≦)ノ
Bruhh the timeline is not set now a days,..... If you trace way way back at age of 12, parents already set up marriage
Even in modern day US, 16 years Olds can legally marry and/or become independent from their parents
They have a 12yr difference and the setting is medieval times, where teenage girls were married off to 30+ yrs old perverts for political and economic reasons add fantasy to it and most "common reasoning" stops existing
Even if they wait for another 3 years, 16 is still not a legal age for marriage.
Idc if the author set the story at that timeline but s/he need to consider their target audience. Imma call the fbi fam. ╮(￣▽￣)╭