Yes, it's true, his column's invocation of Pink and Avril Lavigne is clumsy and unconvincing, and the precise claim he's making about pop music trends breaks down on any number of levels. You can see Ezra Klein, and several posts from Dana Goldstein having good sport with some of these issues. That said, Brooks' observation here is true and, I think, not made often enough:
Now young people face a social frontier of their own. They hit puberty around 13 and many don’t get married until they’re past 30. That’s two decades of coupling, uncoupling, hooking up, relationships and shopping around. This period isn’t a transition anymore. It’s a sprawling life stage, and nobody knows the rules.
This is a much more sensible entry-point into the endless "hooking up" disputes than the standard "what's with all these sluts these days" fare that you usually get from the right. The reality is that technological and economic change has raised the age at which people -- particularly more upscale people -- do things like get married and have children. But biology stays the same. Consequently, people in their teens and early twenties engage in a lot of courtship-related program activities that don't really entail a good-faith search for a spouse.
This is a real and meaningful change from the recent past, that, like any significant, change, is going to have some downsides. Downsides that people are going to notice and talk about, and that deserve a more thoughtful treatment than what you get from Laura Sessions Stepp. Now, I do wish Brooks had spent less time on Pink and more time on trying to reach some kind of conclusions about this, but as far as observations go, it's not a bad one. There just ought to be a maximum age above which you can't casually opine on pop music trends.
UPDATE: Much more from Dana who notes, among other things, that "traditional" patterns of American family life are actually of relatively recent (i.e., post-WWII) vintage rather than representing the timeless wisdom of the ages.