What's a healthy protein amount for my cat? Is Blue Buffalo safe?

Unfortunately, I do not think you are going to get a consensus or simple answer to this question. The short answer is that we think the most biologically appropriate food for a domesticated cat is a mouse. And that is quite high in protein. In a young cat like Autumn wihout any health issues, I do not have a problem feeding a high protein food. Cats are obligate carnivores and generally thrive on a high protein diet.
One thing you have to think about is that if the food is lower in protein, then it will have to be higher in carbohydrates and/or fat. Again, since cats are obligate carnivores, they are not able to utilize carbohydrates effectively and will often just gain weight on foods that are higher in carbohydrates.
You also have to consider if you are comparing dry food or canned food. Dry food will "appear" to have more protein than canned food on the label, but often canned food is actually higher in protein. I feed my cats a rotation of different canned foods and Blue Buffalo is included in that rotation. I do not consider it too high protein for them.
Please let me know if that was helpful. I am passionate about cat nutrition, so let me know if you have any other questions. Thanks for using Petco Pet Education Center, formerly Petcoach.