Varies. Depends on genetics, diet, number of feedings per day, water quality, water changes, tank size, etc. With proper care frontosa can reach spawning size in 3-4 years. Males will grow faster and larger than females.
^This. It really depend on a lot. My current colony started out at .5-1inch range I have had them for almost 4 years. I took about 2.5-3 years for a few of them to hit 8-9inches. I have some in the 6-7 inch range a few still in the 5 inch range. I had another group before this one and one of the frontosa reached 4 inches and it seemed as the years went by she just never got any bigger while the others did (and yes she was eating plenty). It can really depend. Feeding, water quality and water changes are important when they are growing.
Thanks. Tanks size for now 75 gal grow out, feeding sinking carnivore 3x a day, water change 50% every 2-3 days. Is this fine? I've always had SA cichlids wanted to try my hand with frontosas