You should be able to tell around the 18" mark, coloration under the throat and thighs has nothing to do with gender, as our females are brightly colored there as well. The bumps you may be seeing near the vent, could be the wrong side of the vent, as all dragons have this on the one side. Femoral pores will start showing alittle later, give him/her some more time. Females can grow quite the crest too. This is a headshot of my female and her crest