It's not just a stereotype that girls mature faster than boys -- and it's not simply limited to physical maturity. According to one study, boys' brains don't catch up to girls' brains until as late as their 20s [source: ABC News]. Aside from the biological aspect, some observers point to a societal delaying of maturity in men. George Will claims that we're living in a "culture of immaturity among the many young men who are reluctant to grow up" [source: Newsweek]. He cites a study showing that 13 percent of men between the ages of 25 to 34 live with their parents, versus only 8 percent of women.
Even if you don't buy that we're living in a culture that encourages men to extend their childhoods, there are some men who are simply not mature enough for marriage. Age has nothing to do with it, either. They get older but don't "grow up." People who are emotionally immature are generally self-centered, impulsive, overly dependent on others and have wildly fluctuating moods. None of these things are compatible with a healthy marriage, which requires selflessness, patience, interdependence and stability. So if you've seen some of those traits in a man who got cold feet, it might just be the reason for his backing off of getting married. And in this case, it's probably for the best.