I still feed a mixture mainly because i got a full pallet of kibble im not going to throw it away but i do find different types of meat go better for instance if i fed a dog kangaroo that has never eaten it they shit like a black tar and fart like nothing else hahaha... If i feed fresh warm pig meat most will throw it up i have to freeze it first. I tried feed em big wild bird the other day no one would touch it.
But to answer the original question i have a 8 year old dog i still feed him a high protein high fat kibble no way would i cut a dog back to old man kibble unless he was retired and i wanted him die off quicker to free up some chain space...