You said sex doesn’t differentiate until the development of sex hormones (that is puberty or 8-13 for those uninformed when the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are produced in the pituitary gland). Sex hormones has nothing to do with the development of biological sex, before puberty there are already all sorts of things that make boys into boys and girls into girls.
As far as the differences, the genital ridge isn’t externally apparent but the SRY gene is present all along, in mice it has been shown SRY starts expressing just days after insemination. Obviously a gynecologist is not a biologist, they cannot with the naked eye determine the sex yet, nor do they have any interest in endangering the child to test, but it is already differentiating before it becomes externally visible. The notion that until week 8 it’s just a coin flip whether you get a girl or a boy is unscientific bullshit.
You can determine sex from the moment the insemination started developing cells, due to the presence of SRY which is not present in female.
Removing testes does not prevent or invert male muscle and skeletal build, that’s a very old and inaccurate theory. Once you have developed the skeleton of a man, you cannot reduce it with estrogen, at best you get osteoporosis. By 21 your body will neither grow nor shrink significantly, exercise can adjust it somewhat but you’re pretty much fixed. If you remove the testes or give estrogen and puberty blockers to a healthy boy to prevent a healthy muscle and skeletal build in puberty, because you are of the belief his biology doesn’t match your world view, that is just child abuse.
Please stop spouting scientifically inaccurate bullshit.