That should be fine. Just remember that FEMALES max out around 10 inches. Males will mostly hit 12 inches, and max out at around 16inches.
Also, tank size is not what stunts growth, but it is water quality. A smaller tank is harder to keep clean. I recomend a weeky, if not biweekly water change of 20-40% for your red devil, especially once an adult. For mine, I do 1-3 10-30% water cahnges in my 55g tank (48x15x18). When he hits 6 or 7 inches, I will be forced to increase the size of the water cahgnes.
They KEY to growth is a variety of foods. Mine gets Omega One cichlid pellets, Omega One shrimp pellets, frozen brine shrimp, feeder minnows, pinkies, crickets, superworms, Wardley cichlid crumbles, HBH Supersoft Spirulina pellets, Omega One Veggie Rounds, earthworms, frozen bloodworms, and freeze dried ocean plankton. Starting out at under 2 inches at the end of august, he is now pushing 6 inches in length.