I'm 21 and I've always been a loner. Honestly I have no idea what make the average person feel love or a desire towards marriage, so my views are probably a bit off.
Statistically, younger couples are much more likely to divorce, and I would assume the same is true for breakups.
Demographically, people are more likely to have similar sets of psychological morality based on their age. Younger people tend to lean to more selfish traits, or more conventional values.
Those who are self interested in general might view a relationship on a purely beneficial level; looks, money, pleasure of company, or the like. To such a person, the "price" of time, energy, and money might seem like a waste in comparison to the potential a young person can invest to their own desires.
A more contemporary person who prefers to conform to the standards of their peers might marry (whether consciously or subconsciously) in order to fulfill the basic "goals" of a "normal person"; to have a family or to have a partner to show off, in order to appear normal to everyone, or to meet the expectations of their friends and family. This is ultimately only more stable so long as the ethics of society support such. In modern society the template of normality has gradually changed from "everyone has a happy loving family" to "everyone is getting divorced", thus the observation serves as a self-fulfilling prophesy psychologically.
The more "mature" individuals of the earlier generations would mostly fit into the conventional ideals of the "happy family", or the post conventional ideals of compromise and understanding, thus their relatively stable lifestyles.
