You mention the marriages between 14 and 15 year old brides 100+ years ago. These were never about sex, or in many cases even love. They were about family, the preservation/expansion of wealth/land and the benefit to the children that such marriages created.
An experienced/accomplished/wealthy man of 30+ years would court and marry the 14 or 15 year old daughter of another prominent/wealthy family. They would have children who had wealth, land, and social stature.
In these cases these are just perverts....execute them.
I agree with you, but more recently, “kids” did fall in love young and marry. My grandfather was 18 and headed to college and my grandmother was graduating high school at 16 and they married. It wasn’t that unusual in the earlier decades of the 20th century, and they were from middle class families.