There's a tiny bit of fuzziness at the boundaries of many of our concepts, but that doesn't endanger the categories themselves. The real question is why you have decided to take this radically sceptical, deconstructive approach to sex and not to other concepts. It's a little uncertain where the sea turns into the sand but do you try to walk on waves, or sail in the desert? There could be some argument about when raw becomes cooked becomes burnt but do you eat cinders or raw meat? No, you don't, because there's an important practical difference and the exact boundaries don't matter most of the time. And anyway, sex is not a spectrum like thin to fat or small to big. There are two big, very different categories into which almost everyone falls, and a tiny number of hard-to-categorise cases.

Oh, and I can't believe I have to say this, but humans are not bananas. Humans are not merely a set of genes. They're an evolved kind. They're born from other humans. In other words, there's a process and a history involved, not just a list of properties.