Kittens grow the fastest between April and September. During this period, you will find that the cat’s body has undergone great changes. The cat’s development is basically completed by the 10th month. Kittens need comprehensive support during their growth period. For nutrition, breeders should supplement proteins, calcium, and vitamins to help cats grow healthily. Young male cats can be fed raw beef or raw quail when they are 5 months old to gain weight.