male rats are typically bigger then females. so if you have females and are comparing them to pics of males then don't expect them to get that big. also inproper nutrition early in life can stunt their growth. the there is always perception error. you're there with them all the time, seeing them all the time so you don't notice the change growth because its so gradual now. then finally some rats are just bigger then others. i have 4 full grown rats 2 mostly grown rats and a 4month old kid rat and they are all different sizes. kakushi and her mother are really big, spider is short statured and fat, violet is about average and twix and tween are stunted. they're bout 10 months old now and the 4 month old hairless (which typically grow slightly smaller then fur rats) and she's as big as twix and tween. rats, like people, come in all sorts of different sizes