I'm assuming regular WC, good quality params and a low or moderately low stress environment.
I'm assuming that you have the temps at least 80-82 and that the fish are eating pretty much everything you give them. Lower temps inhibit feeding. And undesirable food or stress will reduce feeding or inhibit growth hormones within the fish.
You should examine how much you are feeding (in dry weight) compared to the weight of your fish. You can calculate the weight of your fish using on-line fish type/ length-girth calculators. Imo, you should be feeding fish that are well-past fry stage but not full grown adults in the range of 3-4%+ of body weight in amount of dry weight food per day on average. (Some carnivorous species can eat more at one sitting, but that can be spread out to be one meal of 10-15% every 3-4 days, for instance.) Please note that 1 oz of shrimp is much less than 1 oz of dry pellets in dry weight as the former is around 65% water while the latter is around 10%.
If you are feeding that much (3-4%+) and they aren't growing (and the water quality is good) then the food may have vitamin deficiencies.
Now there are stages where fish growth does seem to slow down. Food conversion rates for fish are not constant from birth to mature size. Of course fish grow fastest when younger, so it's natural that 'speed' of growth will slow down. But actually not growing at all is not a 'normal' behavior for most tropical fish until fully mature. Even then, people suggest that mature fish continue to grow all the time, so that's something too.
Having said that, I'd still be concerned if the actual food amount was too low or was deficient.
