My experience as an engineering student leads me to conclude that less women have math and science skills or that women are less likely to pursue skills in math and science. Lecture halls typically have 90-130 students and 5-15 women, and this at a typical university that is, like all universities, majority female. However, I could just as easily infer that south asian and east asian people are more intelligent than caucasian people who are more intelligent than african people in this regard.
Honestly, it's very tough to categorize intelligence. Neurological studies on brain differences show that women have a higher portion of white matter in their brains (space made up from mostly axons, which are white due to the fatty myelin sheaths covering them) and men have a much higher portion of grey matter in their brains (which is made of mostly cell bodies of neurons). Axons are used for linking neurons and cell bodies are support for the life of a neuron—of course the problem is that no one knows what relevance this actually has to anything, that is to say what purpose a higher concentration of cell bodies relative to axons actually serves, but any good theory of gender-based intelligence should incorporate this observed difference. Due to white matter, women should theoretically be superior on average at linking information than men. But what does gray matter mean?