It'll depend on your tank settings. Heat plays a big role. The warmer your tank (to a point), the quicker your fish will grow. Keep in mind, this shortens their lifespan as well. I have a tank full of guppies that I bred and decided to keep instead of feed to my cichlids. After about 6 months, they are full grown and have all their color. Females will probably continue to grow for a while after that. Hope that helps!