Well, bemused, you certainly bring up some interesting (and valid) points.
Certainly there should be no problem with a child who decides that he is more suited for cabinetmaking than medicine. However, professions like these still require instruction and training for the vast majority of people. These types of schools can be community colleges, state schools, vocational institutes, etc. Of course, it is very unlikely that they will be single-sex. And very unlikely that they will be primarily Jewish–especially if one lives outside of the NY area.
Personally, I think that the solution lies in education at the High school level. Sooner or later, our children will go out into the real world and interact with other people of both sexes, Jews and nonJews. (I realize that there are communities which are exceptions to this.) I personally think that the Orthodox world has carried the separation of the sexes too far–and when they are finally thrown together, many of our children have no idea of how to interact. Perhaps with a little exposure to people of the opposite sex–during high school–say, a mixed mathematics or history class–might be a good idea. They could learn that not every encounter between boys and girls at a social level need lead to an aveirah*. Perhaps then, they could attend a vocational school or college alongside members of the opposite sex, and still keep their eyes and minds on the job–that is, getting an education.
*Yes, I am also aware that there are those who believe that simple conversation between a boy and a girl is an aveirah.