A Munro and Andrew Wood sum up a lot of the points pretty well. Certainly when I was 13, I was sexually inexperienced in many ways (probably like many young teens in the early 1960s). Plus, the whole 'social climate' of sexual mores in the Industrialised East Midlands was incredibly repressive. Apart from smutty talking (maybe masturbating*) with your closest peers....sexual matters were strictly taboo.
* Contrast my ultra - strict, selective Grammar School with today's educational establishments. We were frequently told during RE lessons that 'beastliness' (!!!...viz: wanking) was a filthy, disgusting, sinful activity. Indeed I shall never forget 2 boys who were caught masturbating in the school grounds. They were caned in front of the entire school and then expelled. Is it any wonder we were so sexually repressed??
But...to return to medicals. No, inherently (as the other posters have stated so eloquently ) there was nothing sexual about the experience. Yet....inevitably reflecting on it....I / we had to take ALL of our clothes off in front of the doctor / nurse etc.
And, yes, in those days...they did examine, touch, feel (etc) your genitalia very thoroughly. As I have described in other posts...when Iwas 13, I was examined by a female doctor. She was very professional. But...as a gawky, nervous, teen boy. Oh my.....standing there totally naked with a woman (professionally) 'feeling me up'. I was mortified to begin to get erect. So, not inherently sexual...but there was inevitable erotic tension...which I would subsequently fantasise about.