He said that in reference to coworkers at your job. Some of the women are “mean girls” who gossip about other people, some guys are bullies (obviously not in an in-your-face way), and some of the adults just act like high school students. The only difference is that some of your coworkers are in their 20s, 30s, or 40s.
Would you say thats accurate?
The idea of growing up is broadly a lie or misconception. Some people realize they are now responsible for themselves and perhaps even others, and that is pretty much the biggest change psychologically after puberty. A lot of people don’t have that realization or much great impact from it, so yeah, a lot of “grown-ups” working jobs are not all that different from highschoolers.
There are also marked biological changes that affect behaviour though, like the development of the prefrontal cortex, but I agree: it’s a matter of personal responsibility and not everyone gets there, sadly.