I am uncertain if there is a positive correlation between marriage and age, yet there is most likely a positive relationship between salary and age. Employers desire experience, and seniority in the workplace more likely than not secures the employee higher wages. That's not to say, however, that all elderly job-seekers are guaranteed work. Caplan brought to light an interesting "discrepancy" that may be explained by means other than economists have established a "double standard." For one thing, there may be a large proportion of single, white males that believe marriage would lead to children. The thought of having kids intimidates the college-grads or high income hopefuls from settling down until they themselves have a steady/larger salary. From another perspective, being married with kids could act as motivation for the male to work harder and secure a better job to provide for his family. A wife may act the same way.
While the statistics lead one to believe that marriage may lead to a higher premium, speculation of divorce, along with alimony, is certainly not encouraging. Also, marriages may be a direct result of a man's income. There is a higher correlation of marriages for men with higher incomes than those who merely "get by." The 44% premium with marriages may be an after-effect to an up-and-coming mate's promotion or line of work.
These points are all speculation, however.