From my personal experience this “ought to be” is the problem. Once you get your first job, everyone expects you to drop everything that you’re passionate about and start behaving like an adult. That can be overwhelming and I wouldn’t judge anyone for wanting to keep that cozy feeling of being young for a bit longer. And as long as all important responsibilities still get taken care of, why not let adults be as childish as they want, whenever they want?
Never said that, never meant that.
When I said “inner child” I meant his own capability of leaving his adult responsibilities behind for a while in favor of doing things that society as a whole deems childish. Indulging in certain hobbies, acting a certain way. I can’t find the right English word right now. In German we might call it being “unbeschwert”, so maybe “unburdened”.
I was specifically replying to the passage that he should have spent those 13 years in age difference growing as a person to an extent that he shouldn’t have much in common with a 16-year old anymore. And to that I ask: why? Must every adult be a joyless, mindless worker drone who can’t enjoy the things they enjoyed when they were 16? I’m happy to discuss if the relationship OP described might be problematic because of a power dynamic and that’s been done to death in this thread. But saying he isn’t allowed to feel connected to someone younger than him based on shared interests or a need to escape his adult responsibilities for a while feels bitter and judgemental.
None of this has anything to do with me labeling anyone as an actual child.
Edit: Maybe a picture says more than a thousand words so let me link to my favorite XKCD: https://xkcd.com/150/