Yes, they're surprisingly fast growers. Mine attained 6 inches in about 6-8 months when I bought them at inch size from the store. At this point, they eventually slow down.
Golds grow slightly faster then reds usually but both are sort of medium speed as far as severums go. They grow much faster then rotkiels but a little slower the greens.
I find their growth to be slower than most similarly sized cichlids, but a lot might have to do with their intake of food and stress due to tankmates and other factors like that.