how fast they grow depends on alot of things, how much you feed them, what you feed them, what size tank they have, water temp, and females tend to grow alot bigger and faster than males
this isnt to say that he wouldnt be happy in the 100gal for a little while, but your going to have to keep very close attention to your water params in a smaller tank as he will foul the water quickly, specially with other fish adding to the bio load.