Scott, I just read your other thread and seen the pics.
9 months is plenty old enough, and I have seen older females with the horizontal stripes.
(I have a few females that are 6 months that constantly display them, and they are pretty durn big. Same reddish type base, too.)
Usually it's a stress/defense thing, and in the above pic she looks intimidated, lol.
My Giant Halfmoon was a most gentle daddy to his gal, who was much smaller, and his fry.
First go round with him, I tried a fish that was close to his size (3 inches) and she was blood thirsty. Second time, with the 2 inch female, he fell in love
I do not have any experience with Plakats, though. The large female I first paired him with, an import, arrived looking very much like a plakat. Very aggressive.
Since you were successful the first time, I guess do the involved process, especially since you are breeding for something specific (Horizontal stripes).
I envy people who just get 2 fish, chuck 'em together the day they get them, and they spawn. I'm not that adventurous to take a chance on sentimental or high $ fish.