I have 2 groups of mollies, about 1.5 months difference in age. The older ones are much larger than the younger ones. The older ones are 6 months old, the younger about 5 months old. They are kept in a 110 gallon aquarium with 15% water changes each week. It seems as though when the older group was the same age as the younger group, they were still larger. I am wondering, do mollies produce some sort of growth inhibiting hormone?