Teenage childbirth actually has a high risk of complications, versus birth in the 20-24 age range. (There is an entire WHO page about this.)
The brain goes through a lot of changes between 17 and 21-25. We have evidence of this. It's not just "feminists changing things". One consequence of your brain reaching maturity is that it is harder for people to manipulate you.
Marriage is not what it used to be in terms of economics either. Use your head, man. Fertility does not drop to nothing the moment a woman turns twenty. I say this as a non-redditor. I find it funny how people are so often concerned with female fertility and age, but the babydaddy is allowed to be old as the hills and not blamed for any birth defects, despite that advanced paternal age is associated with many birth defects and fertility struggles.