@rufioh
You are wrong about the fertility window. Female humans are fertile past 25 but after 25 the chance of impregnation gets lower with the month while the chance of genetic diseases get higher, that is what define the "fertility window" which is just the period in which the individual is "better suited" to have a child (higher chance of impregnation and lower change of complications).
Yes, biologically female humans are "ready", as in able with no biological downside, to have children from 14 onward. Whether it is a good thing to have offspring at that age is not something I care about, that is something for moralists and ethicists to argue, but it is not well view by secular societies though still common in the world, usually at the age of 16, but you misunderstood what I wrote anyway. I have not said people should have kids below 18, I said that if what you said is correct and an adult is only over 25yo them biologically the best time to have kids is before being an adult.
Thanks for the sources I will be reading them but from your comment on the fertility window and my reply I'm assuming you didn't understood what they say and just assumed you did.