Every new generation contends with the no longer relevant advice of the previous generation. After World War II, a booming economy made lifetime jobs with pensions the norm. But, by the time Generation X was born, corporate downsizing, off-shoring and the creation of the 401(k) in 1978, made many of the beliefs of the Boomer generation irrelevant to the contempory workplace. Still, Generation X were called “slackers” both because the environment was different and seeing the materialism of their parents did not bring them happiness, they brought in different values.
I think a similar dynamic is in play with the term: “adulting”, which implies the “[husband/w]ife; children; house; everything. The full catastrophe.” Notions of needing to work 9-to-5, car payments, home ownership and so forth are as out of step with the modern work environment as believing in lifetime employment and pensions. Yet, this standard, which is just as bad as the materialist and consumer values of the Boomer generation, is how younger people — albeit in a seemingly joking manner — are encouraged to think of themselves, a social gaslighting designed to birth an imposter syndrome in the young. So, the use of the term is a bit of a crime against the language — being an adult has nothing to do with mortgages, but it’s really an example of the bad ideas mass culture propagates that harm everyone that comes into contact with them.