New Flower won't eat? Help this newbie?

[Mister Ious]

I'm new to the hobby. I'm starting with Flowerhorns.

I purchased a juvenile, a little over 1 1/2 inch long. I've got a few questions here:
1. At about what age do they reach a mature size? Or at least when males produce a more pronounced bump in the head?
2. It's not eating. I just purchased it just a few hours back. Is it normal? Is it just getting used to its new surrounding? When do you think will it be able to eat?
3. I'm keeping it in a 20 gallon tank. Of course I'll move it once it grows to a bigger size. Is that okay? Is the tank too big for it? Becuase it's almost impossibly to spot it in such a large tank.
4. How to distinguish the sex even at a young age? I remember having researched something about the fins. Please show me some pics. Remember, it's only about 1 1/2 inch long.
5.) How much do I feed it a day? I give it specialized flowerhorn pellets. How much/many pellet per feeding and day do I give it?
6.) Do all juveniles have a dull coloring? I purchased a gray/silvery one. Will the color improve with age? Or will it stay the same?

Please answer. I'm only a newbie.