My RBP are 6-7 months old. My largest one looks like he is some much bigger than the other. When I look at them it seems like they have they favorite spots in the tank. Also, it looks like a dominant to less dominant order. Even when they feed. The largest one seems to eat the most. The two smallest one will fight over food. Like if one gets a hold of a feeder the other one try to take it from him. However, they don`t try to take food from the largest one nearly as much.