i have something like this right knowI've had some that get way behind the rest in development. I have one chick whose hatch date is 1-22-12 and is the same size as the ones who hatched 3-10-12 but featherwise the older chick looks like a mini-adult.
I also recently got in the mail from a breeder in WI 4 chicks that hatched 2-20 about the same age as the majority of my 'teenagers' and they are HUGE by comparison.
Either your chick is a dwarf, or is just a very late developer. I've had some like that and it takes them forever to feather out and 'get pretty' but they more often than not are the prettiest birds and look perfectly normal when they reach 6-7 months old.