Dear Ullah, what a fascinating research question with regard to how particular learner variables might affect L2 learning outcomes (although this specific variable cannot be changed by instruction itself)! I would be surprised if no one has looked into this question more systematically yet. I have frequently observed that gender differences are reported in the result sections of L2 learner studies "as a side observation", even if the research topic itself was not gender differences. I also happen to know that FLA is consistently higher among female students. Overall, I would expect L2 learning outcomes in students to be mediated by differences in other variables (FLA, motivation, grit, etc.) that show the usual largely overlapping, but slightly shifted distributions between genders. So gender would not be the cause of L2 learning differences, but "the cause of the mediator causes", so to speak.