It’s mainly driven by gender equality I would have thought. The more educated and autonomous women are, the less they tend to have kids. The most fertile years are spent (quite rightly) enjoying life, getting an education and engaging in productive economic activity. It is the clash of culture with biological reality.
I do enjoy it, but you can see how it compares poorly to other alternatives for the very youthful. Particularly for women.
But this is not the point - it isn't even a conscious decision for the most part to have kids late. Modern life is just set up that way. None of my peers were having their first kid at 20. None of my peers were even in a serious relationship at 20. Most weren't in any sort of relationship.
