I can’t speak for the typical male, but I can speak for myself.
When watching athletes, I might admire their body tone and temporarily lose sight of the play or feat being performed. “Look at those arms/legs, look at that form, that is really amazing and beautiful”. The same goes for dancers, even with teenagers. Most of the time (as I enter my mid-twenties) I don’t lose sight of the performance, and I think about how impressive both the athlete and her performance is. This goes for men, too. Although the thoughts and feeling are the same, I probably won’t use the word beautiful to describe men. Regardless, I do not think about having sex. (unless they are doing some sort of sex-mimicry dance, but I’m not really into that and think it is gross)
To an extent, the same thing happens when I see an attractive woman. It might be her body but more often it’s her face. I think to myself, that is a pretty face or attractive body (or both). Of course I notice, my eyes aren’t shut. I don’t think about sex, and unless it’s some sort of performance I don’t dwell on those thoughts for more than an involuntary split-second.
My father’s advice is to keep the sex-thoughts to your wife and in the bedroom, or other designated sexy places. Abandoning yourself to lustful thoughts in un-sexy places only creates a feedback loop. In the brain, I hypothesize that abandoning your thoughts to lust only serves to strengthen the neural pathways that enable lustful thinking. Whether or not lust is healthy or moral I will not consider (no idea; probably not), but it is certainly socially unacceptable. There might be a way out with therapy, and working with your wife to associate sexy thoughts with sexy places.
All of that being said, it’s not unheard of for teenage boys to say they think about sex the way you describe. I never did but some of my friends did. They grew out of it. It sounds like our friend nate gave in to desire, and it will take quite a lot of effort to “fix” that.
~Max