Most cats are fully grown at 2 years of age. However, some larger breeds of cats, such as the Maine Coon, may not be fully grown until 4 years of age. At 1 year of age, a cat's biological "age" is equivalent to that of a 15-year-old human.
Cats as young as 4 months old may be capable of breeding. Due to the rapid pace of growth during the first few months of life, cats should be fed special kitten food until they are around 6 months old, at which point they can be switched to a regular cat food.
Kittens are weaned around 6 weeks of age but should remain with their mother until they are 4 months old. In the wild, cats often remain with their mothers until they are at least a year old.