The answer is: when they reach adulthood. Ragdolls usually hit adulthood around three to five years of age, with males reaching it first at about four years old and females at around five years old. The average weight range for a full-grown ragdoll ranges from 12 to 18 pounds, and the average length from 15 to 20 inches from nose to tail. Keep in mind that this is an average, and the size will vary from cat to cat. Some may be smaller or larger than this range depending on genetics and diet.