Can women be Makai Knights?
Taken from Garo wikia


  The Order required self-sufficient/independent warriors that's highly adept in martial arts (stronger than their priests and greater combat strength against Horrors), strong mental and emotional discipline (to handle their emotions, manage against potential dark energies, and see through illusions), and mastery over Soul Metal (due to its dangerous nature); creating a full-fledged Makai Knight is a lifetime of training. Because males are physically stronger than females, the order decided to exclude women from ever becoming a knight. 


I'm not sure about other armors, but in Golden Knight's case, one day in every month, the knight won't be able to fight as Zaruba is taking the knight's whole day. Also, women has to face menstruation every month, and that menstruation didn't last just one day and disappear tomorrow. A female Makai Knight would be unavailable for more than one day a month, which is a totally bad idea. Thus, while technically they might be able to become one, it is undesirable.