Is there anything to this comment except No True Scotsman arbitrary gatekeeping? The internet is full of "you don't become a REAL xyz until" followed by a gatekeeping filter which the commenter just made up, something they have passed and people they look down on have not passed.
What about being able to vote and drive and join the military, those are predicated on a legal value of "being an adult" which is a cutoff at age 18. Well we can guess that Saint_Genet really means something about independence and self-reliance, so exclude them. What about a trust-fund child who moves out but still gets money and support from their parents? Preumably the gate moves slightly to exclude those people because having to take responsibility is the REAL filter? And what about people who had awful parents and had to "grow up early" or take care of their parents? Shift the gate around them, too because they're respectable people who should be on the superior side of the gate. What about people who move out, have children, and rely on the grandparents for childcare and support - well they're adults because that's expected and an approved kind of parental support in US culture, no worries. People who moved out, had children, and want the state to fund childcare in some way? Adults? Not adults? Depends on how ruggedly independent and scared of socialism you are. Someone who lives with their parents but is self-employed and employs others whose income depends on the company being well-run, adult or not adult? Judge it based on where they sleep at night, because that makes sense. Someone who lives with their parents and compromises on a shared living situation vs someone who lives alone and has nobody to please or think about but themselves, and pays for a cleaner, and eats out every day? More or less adult?
Draw the gate wherever it makes you feel superior and able to look down on people you just put on the other side. Empty internet status-grab comment.