^ That may sound unbelievable to a lot of people but it happens. One of my very close friends had this problem. For him, love was all about mehboob ki zulfein, ankhein, hont, chaal etc. (as our urdu poets put it) and anything sexual was dirty and baigherti which he would never want to do. 
And this was a fully grown healthy man in his mid-twenties who was under pressure from his parents to get married. Now, he knew about the basic reproductive biology and had a vague idea about the sexual act … but poor soul just could not imagine himself indulging in the act.
The reason ??? I am not sure … but I think the way male and female plumbing is done … it puts some people off to have “playground” and “sewage” in and through same area … if you know what I mean. 
EDIT : oops, forgot to add … this guy eventually got married, has a beautiful daughter now, and all ok in this department.
Apparently, he took 6 months to cunsummate his marriage, but is very happy now. 
P.S - plz don’t get on my case about why we guys discuss each others’ private intimate info. We actually tricked him to get that info. out.