I don't want to put words in your mouth but I think I understand what you're trying to say and I've bolded the sections that stood out to me.
Due to the fact that we have 3.5 teenagers living at home at once (our youngest is 11 going on 19) hubby and I have conversations on a regular basis with them about boundaries, what is acceptable, what is inappropriate, etc. Especially because of what they all see online, all the time. Where you say a 17yr old male has a sexual interest in "almost anything", I think what you're alluding to is how biologically, it is very easy for a boy to become physically aroused. As hubby has put it, for some teenage boys, all it takes is a stiff breeze. This doesn't mean boys are sexually attracted to wind, it just means that physically this stuff can happen and in many cases it's actually rather embarrassing for them.
You say that you don't think for SOME boys, a child causing those thoughts or feelings would be that odd. I can't stand to admit it, but due to the amount of cases where it was a teenage boy and a young child, I believe you are right. For some (and thankfully it's still the minority, and thankfully it's not always acted upon), it's not odd at all. I think case files prove that yes, for SOME, this is true.
Of course it's not "normal" and yes I suspect those boys worry about it and try to hide it because it is not acceptable behavior in our society but the sad fact is, the visual messages they see online and in movies, etc., doesn't help reinforce a positive attitude. It simply validates their abnormal thoughts and feeds them.