To grow baby fish quickly, keep the water warm (28C), is the best temperature for growing tropical fish. When they are mature you can reduce the temperature.
Feed them 3-5 times per day using newly hatched brineshrimp, microworms, prawn, fish and flake. When you feed them, the babies should have fat stomachs and look like pregnant guppies.
Make sure there is an established filter to keep the water clean. Air operated sponge filters are the best for baby fish.
Do a huge water change (50%+) and gravel clean the substrate every day or every couple of days. Make sure any new water is free of chlorine/ chloramine before it's added to the tank, and try to have it at a similar temperature to the tank water.
Try to keep them in a large volume of water. But even in small volumes of water, lots of food and water changes will get them to grow.
Most aquarium fish can be sexually mature and saleable at 2-3 months of age. If it takes more than 4 months to get blue or gold gouramis to 2 inches long, then it's one of the above issues.
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The following link tells you about culturing live food for baby fish and gives a few tips that might help you.