It is not uncommon to see couples where the two spouses are twenty to thirty years apart in age, that is, one third to one half of a lifetime apart. In such cases, it is much more common for the man, rather than the woman, to be the older. Such people include the current, and some past Presidents of the United States (and their first ladies).
Is there a psychological/neurological basis for this phenomenon? For instance, there appears to be a trait called "hypergamy", whereby women prefer richer, more "established" men, to a degree that the man is much older. The converse is that men prefer women who are younger, more attractive, and by implication, more fecund. All other things being equal, of course. Are men and women, in fact, believed by experts to be "hard-wired" in the foregoing, or comparable, ways?