back at the western old day ,15 are the age of marriageable ,you didn't married at that age ,you considered as a homewreck burden ass daughter who didn't marry in the family
which is also in chinese empire in old day ,15-16 are consider adult,same as western old day,15-16 is their debut to the adult world ,you no longer spoiled child that time
perhaps the author,make it based on history age gap between ml and fl(๑•ㅂ•)و✧