I agree, except, today, an 18 year old girl does not know enough about life. In the USA I'd say over 22.
I think a girl is endowed with natural abilities to know how to take care of her husband and children, if she is not corrupted (by feminism, for example). I don't think a girl needs to know much about life in order to get married and start having babies. God has given women the natural ability to nurture and take care of small children. Have you seen a little girl play? Hopefully, this girl will marry a good man, who will be her leader and she can then learn from him. There is much time for her to" learn about life" in the years to come, whereas to have children, time is very limited for women. If a woman lives 80 years (only 20 of them or so she is fertile, so it is better not to waste these precious years).
I think an unselfish disposition and the ability to sacrifice is what is most required to be a good wife and mother. In light of this, I think most modern egocentric girls today are absolutely in no way suited for Marriage. In general, women have lost their ability to find husbands, or keep them. Unfortunately, women are not listening to men; what men want, but other women.
It is the case of the blind leading the blind. I don't see this situation changing until a new generation of virtuous and chaste, high-value women re-appear. What incentive is there for men to marry nowadays?
I realize that my thoughts are not very popular; but this is what I will be teaching my daughters.