Let me put it this way. When I was younger, and we first got internet access, I used to go to Playboy's website and look at the playmates. I remember the Playmate of the Year being Victoria Silvstedt. That was 1997. That means I was 12-13 years old when I started doing this.
Believe me, I knew at that age. If I had been gay, I wouldn't have been looking up Playboy models. In fact, I knew at an even younger age that I liked girls. I may not have been interested in the girls my age, but I didn't really make the connection between my female classmates and the pretty ladies I saw on TV and magazine covers.