am i doing something wrong?

Hi im relatively new to cresties i have one and she is about 3-4 months old. She isnt really interested in live food and when they do catch her eye she struggles to catch them. she is half the size of my boyfriends and they are roughly the same age (his being a month or so older) yet his is twice the size. could i be doing anything wrong?

The growth rate depends on the individual. All cresties grow at their own rate.