Award wining book on Peter the Great shows that because woman needed to have 16 children on average common women started around 12. Huge number of children was because only one in four lived to adult hood true then and earlier in history. All ancient cultures and primitive tribes I have read about start around 12 or earlier because of the huge number of children needed (12 to 16 from sources depending on conditions at that time) Most common people did not get married in church in middle ages, common law (moving in together) was the rule till later.
This does not mean we should do the same but we have to remember the urge to fall in love/ have sex with anyone who has reached puberty is buried down in the instincts needed for a more primitive time.