Oh come on, I only have 8 of them! Haha from my experience with them thus far, they aren't super fast growers, but are pretty steady. Mine were the size of nickels when I got them last year, it's probably been 8-9 months and they are around 3-4 inches now. Most of mine are still young, two quarters, 3 nickels, and a dime (sorry for the weird comparisons, just easiest way for me to size them lol).
I absolutely love keyholes, highly overrated due to their lack of colors, but they have such great personalities in that they follow their mate EVERYWHERE. Mine are constantly together, even when feeding. They are awesome little guys!