It depends on the teen.
It also depends on where you were raised.
I was receiving sex anatomy education by Grade 6, the basics of sex itself by Grade 8, and safe sex techniques all throughout high school. My Grade 9 health teacher demonstrated the elasticity of condoms by stretching one over her hand past her elbow. My Grade 12 CALM (Career and Life Management) teacher gave us pointers on browsing porn without picking up viruses.
Needless to say, everyone in my high school was prepared. The first sex scene I ever read did not surprise me. Still made me blush, but it wasn't like some forbidden fruit I stumbled upon. Oral sex, as long as it wasn't throw in for no reason, would not make me dislike a story.