The age at which cats stop growing can vary depending on several factors, including breed, gender, diet, and lifestyle. In general, most cats stop growing between 6-12 months old, but some cats may continue to grow until they are 2-4 years old. Small domestic cats like tabby cats and Siamese cats typically stop growing around 12-19 months of age, while bigger cats like Maine Coons may take three to four years to reach their full size. Its important to note that cats are considered "full-grown" when they reach 18 months, which is equivalent to the age of a 21-year-old human.