There are several indications that the younger generations of humans (at least in the industrialized nations) socially mature later, many of whom never mature into social adulthood at all. When observing multimedia records of previous generations, the people of the last 50 years (from baby boomers onward) progressively show indications that the need for adult independence is delayed to a later stage. This may be largely due to a cultural emphasis of attaining a higher education to have a better quality of life. For the latter half of the 20th century, many were expected to need to finish high school in order to succeed. In the early 21st century, the emphasis stretched into third level education, and today it is expected of many "white collar" workers to have a college degree for even entry-level positions. Taking the cultural differences into account, comparing the two in terms of absolute years of schooling as a measure of "adult readiness" is not accurate, as a man graduating with a high-school diploma at age 18 in the year 1969 cannot be directly compared to an 18 year old man graduating in 2019, who is then expected to spend at least another 4 years of college education before being given an opportunity to start a career. For an apples to apples comparison, it is necessary to account for the extra years of education required for taking on the yoke of adult responsibilities. A closer approximate equivalent of a young adult of 1969 would be a man graduating college with either a bachelors degree at age 21 or even a masters degree at age 23. In other words, the minds of the men living in these two times are at similar maturation levels when looking at them from a social perspective. But does that necessarily mean that these men at their "adult readiness" age have an equal chance at succeeding in the social expectations of adulthood? Likely not. The world of 1969 is vastly different from the world of 2019, and there's little overlap in the types of skills that would be useful to men of either eras. In addition, neither of these two adults would have an equal chance at prospering in each other's times, as is true when comparing people of any era. Therefore the measure of "adult readiness" is more abstract and difficult to grasp. But I will try to expand on some of the commonalities that can be used to make the comparison easier.
In 1969, a high-school graduate was deemed an adult capable of taking on "adult responsibilities", by getting a job and start pulling his own weight in society. The occupations available to him were primarily local, provided that the economy of that region was in good condition. In general, the types of work available to him with this level of education was quite broad and he only needed to appropriately apply himself to fit the mold. If the man was fortunate enough to be able to go to third level education, then he would have specialized accordingly and looked for work based on that education. This is quite standard and it's the model that's been applied to the western masses at least for the last 100 years. Let us now examine the young man of 2019. When this person graduates from high school, there is a social expectation for him to further specialize in something/anything to be able to sufficiently compete in the job market. This can be an apprenticeship for skilled work or he can continue on to third level education. The duration of this post-high-school learning can typically range from one to six years. So far there's nothing significantly different from the situation that the 1969 man faced, aside from the greater incentive for the extra schooling. But indeed that is the crux of the matter. For those going to college, many often take on large loans to pay their tuition fees, which itself can delay the ability of graduates in being able to be financially independent. Upon graduating from third level institutions, our would-be-employee of 2019 is at least 21 years of age with a student loan debt and likely an auto loan debt. He has yet to begin his adult life and he is already shackled with sizable debt which will need to compete with savings for a down payment for a mortgage (because apparently home ownership is another badge of adult success). If he's from a well-off family then perhaps he might ask for assistance with the down payment, but that only reinforces the argument for juvenile dependency. The net effect of this system is that the 2019 man is not given an opportunity to be in a good financial situation until much later in life. Since financial independence in our society is equivalent to adulthood, delaying it has the same effect as stymieing the transition to adulthood.
On the relationship front, the man of 1969 might have spent a few years "playing the field" before settling down with a missus. He would marry young, have several children, get a house and perhaps repeat the process several times throughout his life. This model cannot be applied to any responsible bachelor of 2019 until he is at least in his 30s as the financial pressure for marriage and family is just too high. If he knows this in his mind then he would delay the transition to adulthood - the kind that expects to take on the responsibility of raising the next generation of youngsters and of taking care of the elderly. The consequence is that the man spends more time doing the things that a family man would not be able to do, which does have its advantages, but they may not necessarily be the types of activities that a parent or a "responsible adult" would engage in. But aside from financial reasons, there are other cultural, social, and personal reasons for not starting a family at an early age. Indeed those factors could very well have a larger impact in the delay. However, it must be recognized that becoming a parent is a natural process for any living creature, including our very special hominid(s). Delaying it involuntarily through monetary pressure is different from choosing not to settle down. The psychological impact of this artificial hindrance must be considered and its knock-on effects examined. The process could be modeled as an environmental impact on the psychology of the individual, triggering behaviors that incur hormonal changes to accommodate for the mental shift. The argument is conjecture, but it's plausible as psychosomatic responses have been observed to impact stress and hormones. One notable example observed in nature is that of domesticated pigs. When the hogs are released out into the wild, they take on the characteristics of boars by becoming very aggressive, growing tusks and a coat of thicker, longer fur. Conversely there have been cases of domesticated foxes taking on neotenous characteristics through multiple generations of breeding in captivity. If these occurrences are readily observable, then we must consider the possibility that our psychology, driven by our environment, can impact not only our behavioral characteristics but perhaps may even incur physical changes through hormones. It is possible that we may still be undergoing our own form of domestication and neotenization within the confines of our social environments.