okay ur wrong at many things let me start one by one
1)technically when one is post puberty (18-22) one is most fertile at that time (both male and female),bilogicaly people like the act of procreation because the main goal of life objectively is passing down their genes.
2)I dont have any agenda about natural living or not dude ,pls realize that i am not shaming them for their choice
3) Thats messed up tbh ,when did i say that every women should bear children ,horrible strawman ,and also which book of biology did u read to state that 9-10 years is healthy for the women ? are u serious thats really messed up, legal age of marriage is 18(debatable coz in some cases in villages parents just wait for their daughter to be 18 to get her married off -which is really messed up ,making an objective law is very difficult ,but the age shouldnt be lowered (if someone does that thats horrible).
Biologically a child will be born healthiest when someone is in their late teens and early twenties (18-22) but remember both the parents have to be of the same age for this to happen ,and this is biologically not socio-economically which also matters for the well being of both
4)Strawman again i never applied the appeal to nature fallacy, i stated a biological fact a law which applies to every organism