It shall be unlawful for any person to possess, harbor, shelter, or keep adult cats in a greater number than can be cared for in a sanitary and proper manner, or in a manner that because of the number of such cats, such cats create a nuisance as defined in § 7-3 of this chapter, or in a manner that because of the number of such cats, such cats constitute a threat or danger to the surrounding environment, including native wildlife and the property of surrounding property owners. An adult cat, for purposes of this section, shall be a cat over six months of age.