To say a bit more on Mark Regnerus's brief for young marriage, these arguments have a tendency to sound like a debate Ward Cleaver thinks he's having with Paris Hilton. That's not as dismissive as it may sound: Cleaver and Hilton both have points. But they're not terribly useful points.
Regnerus gets at, but doesn't correctly articulate, a genuine problem: A person's 20s are a crowded decade with long-term implications. They're simultaneously the best period to start a career and to start a family. Regnerus isn't entirely wrong to bemoan the fact that marriage has been decisively shifted to the late-20s and early-30s, but he doesn't do a good job integrating his own evidence. It's accurate to say that there's a substitution effect as people prioritize education and career. Plenty of promising college relationships crash on the shoals of law school acceptance letters. But he doesn't get into why they do that, and he doesn't consider the counterfactual of what would happen if they stopped. One obvious example: There's a correlation in the data between young marriage and eventual divorce (see the graph below. Source.). A woman who sacrificed a career for an early marriage would be much worse off after an unexpected split.
Additionally, you actually can have children in your 30s. After 35, it gets harder, but it's doable. It's extremely hard, however, to begin building a career in your 30s. And it's even harder to begin building a career in your 30s with a six-year-old. Again, you're dealing with a tradeoff. Regnerus laments that early marriage is being traded away but he doesn't actually argue that the trade is irrational.
The interesting thinking on this subject, conversely, comes not in judging the trade, but rendering it less necessary. There are times, as Michelle Goldberg has argued, that liberal social policy is the only life raft available to traditionalists. Asserting that women shouldn't choose career over commitment is, to put it lightly, not working. But there are a variety of policy interventions that would make it less necessary for couples to choose career over commitment. For instance: Child care, paid maternity leave, early childhood education, career training, educational help, flextime policies. The question is not how to change the choice couples make. it's how to reduce the need for that choice.
This is one of those issues where you could imagine a pretty fertile compromise between traditionalists and liberals. Both would presumably want similar policies, albeit with different expected outcomes. But so far as I know, there's fairly little intersection between the two camps. The traditionalists seem more interested in scolding women than in changing outcomes. Liberals are correctly allergic to the judgmental take of traditionalists. But liberals, at the end of the day, are the ones with the toolkit for addressing the problem, not to mention the political power to do so. Which gets to a question for the traditionalists: Is this about changing outcomes or changing values? If you believe this is about getting people to make an appropriate moral choice, then exempting them from that choice obviously doesn't solve anything. But if you believe it's about easing the path for families, then that calls for a rather different approach.
Related: Karen Kornbluh on juggler families.