The phrase "appropriate age" means the right or suitable age for something or someone. It implies the age at which a person is considered ready or capable to handle or understand certain things or engage in particular activities. Full definition
If you haven't already, you may want to ask your veterinarian for recommendations about neutering your dog, especially with regard to the most appropriate age for the surgery. (barkbusters.com)
Using pacifier at appropriate age is often on top of mind and regular use past the preschool years can have negative affect on oral development. (newbornbabyzone.com)
We require that kittens are spayed / neutered when of appropriate age and health. (halfwayhomepetrescue.org)