A few more details would be nice. Typically a field contains a discrete piece of data so you are asking a field to track 2 pieces of data. Can you have 'Read a book in the last 3 months' with the same criteria? or 'Read a children's book in the last x months' again with the same criteria? If so then I think the easiest may be to add a field to store your male/female data bit. Could be set up as a checkbox as well if that makes it easier for you/your users to make it work.