A kitten's age can be estimated by observing his physical signs, weight and behavior. The eyes are almost completely open at about one week, and a kitten can usually walk by the time he is 12 days old. By 20 days, he should be using the litter box and eating solid food. A kitten is usually friendly and sociable with humans until he is about 7 weeks old.
Determining a kitten's age is crucial for socializing him properly and caring for him. Weight and size can vary, but a kitten should gain roughly 4 ounces per week. Once a kitten is 8 weeks old, he is much less likely to allow humans to approach. Socialization should occur between 2 to 7 weeks of age and is integral for helping a kitten become accustomed to sights, sounds, smells and other animals. Mishandling during this period can result in a fearful and easily stressed cat, while proper and pleasant interactions can result in a friendly and well-behaved adult.
Hand-rearing a kitten is a time-consuming process. The kitten is weaned at approximately 3 to 4 weeks of age and slowly learns to adjust to solid foods. Although he is mobile by this age, the kitten is still susceptible to hypothermia and hyperthermia. By 5 weeks of age, the kitten should be playing with littermates to learn proper cat behaviors.