>adolescence extends to much older than 18 or even 22 years

Adolescence extends to a few years past when you start being treated like an adult, for some it can be extended almost indefinitely.

People increasingly want to delay being treated like an adult until after a person has reached the full maturity of an adult not realizing those two things are linked.

The transition of this happening too early or too late leads to many mental illnesses where your brain is being wired to expect and react to the world incorrectly and when most of the rewiring is done you're somewhat stuck with what you've got. (If you're pampered and protected for too long you can't handle anything but that the rest of your life, if you face adult challenges too early you develop maladaptive strategies to cope with things you can't handle, etc.)

The "25 year old adolescent" is a troubling development.