In what sense? My wife and I certainly planned our first child very young (for the US at least; internationally, we were on the late end, like most Americans)
I suspect the increasingly shrinking demographic of churchgoers is different in this regard from the rest of the population. I think they're right in saying people who plan typically don't plan children for before 30, I don't know anyone near my age (early 20s) who is doing that; many don't want children at all.
My wife and I plan to have all our kids before 30. We're doing well above average financially, and we want to be young while our kids are young. She is currently pregnant with our first.
It helps that she is not very career-minded, I have the opportunity to work from home, and I'm working a role where I earn well and never need to do overtime.
That's the difference. Couples that plan explicitly typically don't plan their firstborn before 30.