I do tons of things that many people consider juvenile, but which I think have been either labeled that unfairly, or which I believe have value for adults despite being child-friendly or even child-targeted. As an example intended to portray my perception of the situation, children eat bread. This does not mean that there’s anything wrong with adults eating bread, and if a bunch of people (or even most people) declared that eating bread was juvenile, I would consider them wrong and do it anyway without worry or embarrassment.
Anyway, now that I’ve preemptively said that anyone who could possibly criticize me is clueless, here are some of my “juvenile” interests:
Cartoons, mostly ones make from the '70s and later. I don’t like all cartoons; I require them to have merit on their own from standpoints of art, writing, and characterization. I do adjust my expectations based on the era the show is from, though; the classic He-Man was a horrible show by modern standards but considering the budget, production constraints, and expectations of the era it was under it was remarkably good (though She-Ra was better, despite the pastels, due to the heros operating from a position of weakness rather than strength). And yes, My Little Pony: Friendship is Magic is a remarkably good show, by a large number of metrics.
Transformers - the toys, that is. I like the engineering and the collectibility. Well, mostly the engineering. If it takes me ten minutes to manipulate its dozens of little parts to convert it from one mode to the other, with both modes looking exactly as they should and hiding the other, that is a good transformer. Though simpler ones are fun to fiddle with too, transforming them back and for just to give my hands something to do.
Legos - For these it’s mostly the collectibility and display value, though I do like the assembly process as well. (It’s like making plastic models, but you can enjoy the assembly process repeatedly.) I don’t free-build, and while I have made a small number of original models (designed using CAD programs), mostly I don’t have ideas that are both interesting enough to attempt that are also technically feasible.
Young adult fiction - When I read book I’m interested in characters and their motivations more than the plots and adventures. I like drama. So both books for adults and books for kids may or may not be interesting depending on what’s between the covers. If anything young adult books seem a little likelier to focus on characters than boring crap like politics and other people’s sex lives.