I’m guessing it was sometime after family explained to me, there are girls & there are boys in this world (nothing anywhere near heavy), my mind concluded all cats were girls & all dogs were boys, all by itself!. Not sure when/how that was made clear. I’d come to many conclusions when I was little & was correct about several crucial matters ‘going on’, without the language to express them to anyone. I’ve since developed expressions unique to me about my small world, when I was little.