I hate the idea that we're just supposed to naturally "grow out" of things

Pretty much the title. The idea that there are things that naturally just go away the older we get is absurd. Like that doesn't happen. Is it supposed to? It shouldn't. 

Like, I've liked My Hero Academia since I was 14. I got attached to the characters, got my first real fictional "crush" out of it, all that "cringe-core" kinda stuff. Now I'm 20, and none of that really went away? And when was it supposed to? I mean just the fact that I'm 20 already just feels wrong and unnatural to me, like none of the past few years even really happened. I feel exactly the same as I did when I was 15, but am I not supposed to?

And just the mere fact that getting older means some things aren't meant for me anymore...I just don't like it. Like even if it's not necessarily weird for me to like something, the idea that I'm not the target demographic anymore just sucks. Especially when it feels like I literally just was the target demographic, but now suddenly I can't be just because a little bit of time passed. And even the fact that I have a problem with it might be weird? As if the fact that it all didn't just go away on it's own is itself a problem. I can't control that, and even if I could, why would I want to? There's nothing left after this anyway. Life after turning 18 is all just straight downhill, but I'm not even allowed to be upset about it?

I dunno. I just wanted to rant.