I started when I was like.. fourteen or fifteen, so that I totally get. No one else wanted to read the cat books and actually laughed at me for it quite a fair bit. I suspect a couple of my friends know what it is, but don't read it or want to admit they read it.
I distinctly remember going through great pains to make sure that no one at school saw what I was reading. I'd always hold the book so the cover wasn't showing. Once someone asked me what I was reading and who it was by, and I was pretty relieved that she'd never heard of it. I told a couple of close friends about reading the series, but they were pretty indifferent to it. I did see two different people reading Warriors at my high school, but I was too shy to talk to them.