I find myself believing that the people who think that these characters aren't acting like adults are either children themselves or are very young adults with little real-world experience. Because the idea that they're not acting like adults is simply untrue.
Lots of adults are emotionally repressed, held back by lack of confidence, unsure what the right next step for themselves is, etc. In fact, for a lot of adults, the situation is worse than what kids have to deal with. Unlike with kids who are simply nervous and inexperienced, adults will get caught in a multi-year "rut" and as a result end up losing perspective on how to move forward. When they do get a chance to move forward, they won't know how, because they'll be years out of practice.
For Tokita, these character traits have literally been spelled out: In the chapter where Tokita's boss interviews him, Tokita established that he gave up on his goal of becoming an artist in university because he didn't have the confidence to believe that he had the talent to make it in that field. He then became a layout editor solely because that was the job he happened to get, and then he stayed at the same company until that company went under. Then, when his company went under, he just kept doing the same work as a freelancer rather than trying to come up with any sort of long term goal or plan. And the only reason that he happened to move past being a desparate freelancer is because when GOSH started up again, Kaji reached out to him and asked if he wanted his old job back. His boss even pointed out during that interview that Tokita has no confidence in himself and can't recognize any of his achievements.
And that's not the only time we've gotten in-story indications that this is a big problem for Tokita. In an early chapter, before he gets his job back at GOSH, he mentions that literally the only socializing he did at that point was occasionally drinking with Kaji, and that beyond that he had become entirely isolated. In this chapter, when Miyoshi attempts to feed Tokita, she mentions that it's been ten years since he's experienced something like that, heavily implying that it's been a decade since he had any sort of romantic relationship with someone.
Everyone here should know that there are a tonne of adults in Japan and the world at large that are "stuck", anxious, and isolated. It's fine to not like those stories -- everyone has preferences and if someone only wants stories with well-adjusted adults more power to them -- but the assertion that this isn't how adults act is at-odds with reality.
