Honestly, even in your late teens, if you acted like an idol otaku...

You wouldn't be treated like a proper human being. At school, you'd be straight-up prey.
It went beyond just being called "pretty"—if you started talking about how their vocals were or what their lore was..
Even in your 20s or 30s, especially in your late 20s, if you did that, people would call you brainless.
But at some point, that culture disappeared, and they even came up with the bizarre term "uncle fans."
Who do you think started that? I think Wonder Girls and Girls' Generation were the pioneers of the "uncle fan" phenomenon.