Like you said, there is a spectrum of psychology depending on the person. Though, in general I wouldn’t think of it as pathology or fixation, and the temptation to do so reflects the depth of the stigmas which say, tautologically, that: men cannot be feminine, adults cannot be children, cis cannot toy with gender expression, and so on. That a cishetero man who paints his nails might be perceived as fixated on femininity — in my opinion, this says something about the observer and not about the man per se, as the observer would be projecting a boundary that the man might not perceive. Likewise, we shouldn’t construct a framework of pathology to contemplate adults behaving “like children” unless there is a clear, well, pathology i.e. there is genuine dysfunction. (Not saying you are doing this, I’m sure you understand)

On the reverse of the medal from “childlike” adults, many adults — particularly parents — exaggerate the difference of children from adults. It’s normal in society to think of children almost as a different species entirely, until they pupate and finally metamorphosize into an adult in discrete transitions. Hence for example, the concern about kids degrading their attention spans on social media does not apply also to adults, despite more or less having the same brain structures and reward pathways, albeit more developed. I think this is a similar reasoning to the notion that kids need emotional validation and should receive it from media, but adults do not.

I’m getting sleepy so kind of lost my train of thought, but close enough.

Edit: oh I was going to say something about the strong separation between child and adult having to do with the requirements of capital, having a clear separation between human beings according to their working status (which of course also includes gender). This has historical roots/baggage in the old feudal understanding of age which was different because labor was different, but inheritance was a lot more important so people had to “come of age” for political-economic reasons. Also there is the instutution of marriage which, in feudal times especially, needed clear (and gross) definitions of when girls as property could be legally sold off to another “commodity owner” which also has Inheritance implications.