Time wise. Its subjective depends on a lot of circumstance. Tank size , foods temperatures, water quality. I have some that are starting to show mature colors that are 6 months old give or take a week or two.
Size wise. I have noticed some of the grow outs I have raised showing maturing colors around 3 inches and mating behaviors around 4 inches.
I say around, because it could be sooner for some and later for others.
The fish I have growing out in larger tanks are a bit bigger and grow a little faster than the ones kept in smaller aquariums.