Kittens start to loose their teeth around 4-5 months of age. You might never notice. I happened to be around while my kittens were losing some of their baby teeth. When they start to move their jaw a lot, constantly licking, clicking then they have some loose tooths that are ready to come out.he age when teeth start to appear can be influenced by breed, environment, nutrition, and season of the year. Kittens will start to lose their baby teeth when the permanent teeth begin to erupt, usually beginning around 3 to 4 months of age.