Ragdoll kittens should be at least 12 weeks old before being put up for sale. They should go through the necessary learning and adjusting experience together with their mother and siblings until then.
After 12 weeks, the Ragdoll kitten develops a better immune system and is able to adjust better to a new environment or home. It is cost saving for the breeder to sell it earlier considering how much it eats from 8 to 12 weeks. But, it should go through the necessary kittenhood stages prior to leaving the breeder's place for ensuring proper adjustment and well-being at a new home.
A Ragdoll cat is normally laid-back, friendly with humans and big with a lighter body color compared to its ears, legs, tail and face.