Complication from pregnancy is the leading cause of death in 15-19 year old girls, and second in 10-14, only because many of them are not yet able to conceive. We have excellent data on this.

Later marriage/first pregnancy is clearly a good thing.

https://www.who.int/health-topics/adolescent-health/pregnanc...

When I looked up causes of death in Nigeria, malaria blew away anything maternal related[]. Not that I would want to die of either.

Another big one was HIV/AIDS. I guess it depends on cultural factors whether early marriage might reduce the number of partners that could introduce HIV/aids. If non-married people are less monogamous it's conceivable the increased risk of HIV/AIDS could overpower the risks of whatever additional childbirth is associated with marriage.

Also note pollution was one of the bigger risks present in Nigeria. So as people get educated to go slave away in a factory it might actually be worse for their health than staying at home and marrying into some pastoral herding tribe or something.

[] https://ourworldindata.org/profile/health/nigeria

I completely agree, but there's a decent chunk of people out there who don't.