Knowing a kitten's age is the first step to knowing how to care for them and what to anticipate.
Remember that all kittens are different. Because each kitten will vary in health and size, physical traits such as weight or appearance are not always a precise indicator of age. Developmental traits such as the presence of teeth will be a more precise way to determine the kitten's age.
For instance, an emaciated 4 week old may be the weight of a 2 week old, but will have her canine teeth.