If you are woman and want kids, biologically speaking, your twenties are the best time to make that happen.

He talks about "These days, kids tend to happen in your thirties." That tends to work fine if you are male. If you are female, it gets vastly more complicated to put off kids until after age thirty. I have to wonder how old his wife was when they started having kids. Most hetero relationships tend to be older man, younger woman. Men can easily put off becoming a parent until their thirties, in part by marrying a younger woman. That works less well if you are female.