Age dating difference
This largely has to do with having social circles that generally include peers of similar ages and being attracted to others who are similar.
Similarity entails many things, including personality, interests and values, life goals and stage of life, and physical traits (age being a marker of physical appearance).
That is, the extent to which someone has "good genes" — indicated by their attractiveness and sense of energy (also known as vitality) — and the extent to which they are a "good investment" — indicated by their status and resources as well as their warmth and sense of trust.
From this perspective, it's thought men's preferences for younger women and women's preferences for older men relate to reproductive fitness.
But because the building of resources takes time, we tend to acquire resources later in life and so are older by the time we have acquired enough wealth and resources to comfortably provide for others.
So, women being attuned to status and resources might explain why some women may be attracted to older men.
But some studies find the relationship satisfaction reported by age-gap couples is higher.
These couples also seem to report greater trust and commitment and lower jealousy than similar-age couples.
Some suggest a lack of, or a reduced pool of, suitable age-similar mates may bring about same-sex coupling with large age differences.