I really don't think that I agree with this, on either count. DW is 2-1/2 years older than I am, and we're pretty similar in terms of education level and overall intelligence (what can I say, smart women turn me on), and I'd say that our marriage has done pretty well, all in all. Although, on average, men may mature a few years later than women, there are wide variations in those averages, among both genders. I also find it odd (or maybe I don't) that the headline writers picked up on the 'younger' part, while ignoring the 'smarter' component.
I'm only 14mos younger than my husband, but I am smarter than he is, lol, and we're still going strong after 10 years of marriage, so I don't think age is as important as are other factors in determining marital success.