Why does most anime feel so juvenile? I get that "it's just a style of animation, there's a ton of diversity," but everything I've heard about or seen feels like it's written for below-average young adults. It's always set in school with teenage characters, there's always random bullshit fantasy elements (or at least enough to give the MC some dumb superhuman power so he's "special" and "cool"), and, if there's any philosophical "theme" or meaning to the work, it's always shallow, surface-level shit that's explicitly spelled out. It really feels like YA for people who don't try to pretend to read (no offense to the weebs in this thread).
I mean, 'Shonen' literally means 'Young Boy', so I don't know why you're so shocked. If you feel its too juvenille for you, go with shows/manga marked 'Seinen', which literally means young man. Its for the demo 18-40. I don't know why you're so confused about this, everything has a target audience. Shonen is always going to be more popular because its a lot simpler. And there's a lot of good Shonen out there, you just have to know your tastes.
There's also a ton of copy-cat garbage too. Some things will ride off the popularity of others. The thing is, even anime trash is better than Western trash, which is why its so popular.
Anime is (I don't care what anyone says) still very difficult to get into if you didn't consume it from an early age. You'll see newfags CONSTANTLY recommend the same anime over and over and over. Such as people who recommend 'My Hero Academia', 'Demon Slayer' or 'Attack on Titan'. They literally have no idea other anime exist. People who have been consuming anime for a long time know what they like and there's so many different niches its going to be hard to figure out.
If you want to explore anime/manga without really knowing much of anything and just going off random recommendations, you're going to have a hard time. Its like with any new hobby, you have to sift through a LOT of stuff. Its not really anything like Western comics or cartoons, which are largely similar (every 'adult' cartoon is badly drawn and badly written comedies, and every comic is pure faggotry capeshit that repeats over and over again). Which is pretty much why you can see fake fans a mile away because they only mention 2 or 3 extremely popular series and never watch anything else.
Also anime is fun because sometimes you get to view your culture through the eyes of another culture. Like watching Japanese writers try to figure out Catholicism is always hilarious to me. Or what other countries are like. (And you will notice a trend where somehow Japan is literally the center of everything ever a LOT, but tbf American entertainment always does that shit).
Honestly, the easiest way to figure out what anime you like is to figure out what stories you like in general. Its not like picking DC or Marvel, or The Simpsons or Family Guy. Do you like science fiction? Sports stories? Period dramas? Action/Gore? Weird shit? Those are the sort of questions you really need to ask yourself or you're just going to end up frustrated and confused.
EDIT:
I forgot to mention a VERY important point: Anime is there to sell Manga and Light Novels, not vice versa. In the west, novels and comics are there to sell TV and Movies, which is why generally anime and manga are better, because they stick very closely to the related source material (though that doesn't mean things aren't cut out for time or budget). So you can read a manga and watch an anime, and while they might both be good and share the same plot, they'll be different experiences.
A second thing to consider, which is VERY important: Was the manga finished by the time the anime came out? This can matter a great deal, where sometimes an anime will be made before a manga is finished. I've noticed its less common now, where you'll have a full season and if there's not enough material, they'll hold off and not do 'anime only' stuff (because a lot of the times it really fucking sucks).
This is another difference too. If an anime is not wholly original, deviations from the source material are generally not good. Anime is very rarely just created whole cloth with no manga or light novels, but these projects can turn out spectacular (
ID: Invaded and
Psychopass). This is because studios are used to doing adaptations, and adapting and making something new are completely different. Just look at 'Game of Thrones' for an example of that.
Honestly, 'anime only' content is a lot rarer now than it was in the past. Even if a manga author loses their shit and intentionally burns their manga to the ground (or conversely, the ending is really fucking retarded. Which still kind of pisses me off that studios won't change retarded endings at all because they've become a lot more gunshy. So a great manga with a fucking awful ending will become a great anime with an awful ending), the studios will still stick to the source material (See:
Attack on Titan,
Food Wars and
Platinum End). In the past, when a manga wasn't finished and they were doing a show, they wouldn't wait. And it didn't turn out too good. A victim of this was
Akame Ga Kill! which is extremely different from anime to manga. The anime, once it runs out of material
just begins to kill the ENTIRE cast off one by one. And it kind of sucks, since the manga itself finished and got a sequel and prequel, which wouldn't make any fucking sense if made now because
people that are alive are dead. And unlike America, shit very very VERY rarely gets remade unless its wildly fucking popular. Because even nowadays, anime is really fucking expensive and takes a long time to make.
Again, its the complexities of the hobby that you really don't know about and can be very confusing if people just list shit off without context.
