Frequent water changes, frequent feeding and warmer temps help with growth. I have two golds that I bought at 1 inch in April. They just mated about 2 weeks ago. The male is about 5.5 inches and the female is about 4.5. I should add, the growth appeared slow for the first few months. I was begining to think I was doing something wrong. Then they seemed to double in size the last 2-3 months. I feed pellets at least two times a day and frozen blood worms almost every evening. I do a quick gravel vac once or twice a week (or as needed if I see lose matter) and a 25% to 35% water change weekly. I keep my tank around 78 degrees. Also to consider, do you have males or females? The male in my tank definitely grew faster.
Idk I keep my tank clean, other than when I had it over stocked for 2 weeks. But, as far as
If they are male or female idk. The gold has had a much better growth rate than the green. I bought the gold a little over a year ago at .5 and he's about 4" so maybe he will hit a growth spurt. But as far as the 2 greens I have in my moms tank they are already as big or bigger than my gold and I bought them at 1" no more than 3 months ago