Gendered Dragons

I am reading Dealing With Dragons, by Patricia C. Wrede (1990), which I just picked up from the library where I'd put it on hold. I don't remember now why I put it on hold, but someone must have said something good about it on the childlit listserv at some point. Anyway I don't know what the precedent is regarding the gender of dragons in fairy tales and fantasy, but Wrede's apparently get to choose their own: "Five of them lay on or sprawled over or curled around the various rocks and columns that filled the huge cave where Cimorene [our heroine] stood. Each of the males (there were three) had two short, stubby, sharp-looking horns on either side of their heads; the female dragon had three, one on each side and one in the center of her forehead. The last dragon was apparently still too young to have made up its mind which sex it wanted to be; it didn't have any horns at all."


I wonder when one is old enough to make such a decision.