We had one like this once - from the RSPCA! They told us the kitten was thirteen weeks, but when we took her to the vets for her first health check/vaccination, he said she was probably only about eight weeks. He doesn't like kittens to leave their mothers until they're around ten or eleven weeks.
She was always a very small (but very healthy and very dominant) cat, who got herself into more than a few scrapes and must have used up every one of her nine lives before she had to be put to sleep at eighteen years of age (senile dementia).