This is an oft-posed question to unmarried, not permanently-situated young adults in their mid-20's. Talk about posing a personal question! The subtext is almost "when are you going to start having children and being responsible, for a change?"
Some of it is due to the fact that at one time young adults married earlier: 22 was the average age for men, 20 for women. Nowadays, it's close to 28 for men and 25 for women. In other words, there's a layer of intergenerational perspective differences to start with. Older people had gotten married at an earlier age; they assume that it's still the norm.
But there's some other things going. One is the envy of the unmarried young adult being free of responsibilities. It's disengenuous to assume that working at an entry-level service job (like a barista) provides the material resources for being really free of responsibilities. And for many of us, there are the student loans to pay back. Most of us manage. Somehow.
There's even the cohabitation issue as well. Eeek! A girl living with a guy! The incidence of unmarried cohabitants has increased dramatically in the past 20 years. As a result, some elders perceive that there's all this wild sex going on. In reality, the fact that a man and woman are living together does not mean automaically that they are having sex: some might be lovers, some might be friends with benefits, but a sizeable number simply are roommates! [Yes, even sharing a bed with no sex. Supposedly married couples do that too. :-)] Still, there's the excessive fear of premarital sex. Sufficient to say, if a man and woman are living togther, most of us Millenials assume that they're also sleeping together. And it's no big deal!
The process of getting an education in part of it too. First of all, few individuals complete their undergraduate studies in four years; if they work part-time (as many do), it may take five or six years. Secondly, there's graduate school. Depending on the level, this can run four or five more years. At no time in the student's career is he or she living a ostentatious lifestyle! Graduate student life is somewhat halfway between the old 1960's-type settled down life and college student life without the frat parties. First of all, some are married and even might have young children. secondly, there's a desire for small comforts, like dining on nice plates, relaxing at the shore rather than the rowdy Spring Break experience, having a lover, keeping a pet or two. Some I know would even aspire to the Rotary Club, if they qualified. And one is a deacon at church.
A desire for travel is another factor. It's really easier to travel if you're single and casually employed. Certain occupations take a dim view of workers who take extended periods for travel.
Even those young adults who are working usually are given entry-level salaries. Even when a couple's resources are pooled, it might not be enough. It's awkward for a couple to live together in one of their parents' household, so they often live separately and look for the occasional prospect for privacy. Some parents actually abet that by making themselves scarce around those occasions. [I hope this is not too surprising a revelation.]
Anyway, it's not just the Otakus who live in their parents' basements; even engaged couples might. I think it's a form of family resiliance that families can be flexible about their moral judgments when circumstances force them to be.
There is some money that has to be accumulated to purchase the materials for a household: furniture, appliances, health insurance. cars, and so forth. Plus there's rent. In the meantime, millenials are in a state of flux or transition: approaching that "settled down" condition by increments. Some household items, like chairs and sofas, might be literally cast off. There's a end-of-semester furniture scavenging that goes on in some university towns.
Of course, the biggest determinant is pregnancy. Babies impose nonnegotiable demands. That's when the traditional settling down occurs.
There's some good news to consider: Couples who marry when they're older tend to have more stable marriages.
57 minutes ago