Trying to Get Sunny Boy to Chew

Sunny Boy is a Goffins Cockatoo and is 8 years old. He isn't very destructive which is good and bad at the same time. It's good because it makes for easier cleanup and it is bad because it is natural and healthy for him to chew. I adopted him almost 6 months ago and I've had no luck with getting him to chew on anything other than my fingers and things that he isn't supposed to.