I think the author is comparing apples to oranges. The author’s point is that people with longer marriages are more likely to survive, which I would agree with, but the same could be said about a couple who married late in life and had a twenty year marriage as could be said about a younger couple who had 20 years in. What about all the couples who married in their 20’s and divorced after 5 or 10 years?
Actually one of the authors points was that the longer you wait to get married the more likely you are to bring the baggage from your previous crash and burns to your marriage, because you will have a lot more of them.
The longer you wait to get married, the more likely you are to crash, as a general statement is not innaccurate. It is more difficult the older one gets to get over the selfishness that a lifetime of being on ones own can bring. I'm not saying everyone who marries older crashes, just saying its a tougher adjustment and many fail to make it.