This will answer some of your questions...
http://web.archive.org/web/20050404212053/...ary.asp?page=20
Tomas.
I'm a bit cynical when dog food companies such as contained in the above link do write-ups and 'scientific studies' on what we should be feeding geriatric dogs!! They're in it for the sales, aren't they? The more different types of food they produce and can market to people with old dogs, young dogs, small dogs, big dogs, dogs with skin troubles, dogs with anything else you could possibly think of (and I see now you can even buy breed-specific foods!!) then presumably the higher their sales are. Fifteen years ago none of this stuff existed and dogs did perfectly well without them.
So in answer to your question, if you're a BARF feeder then I don't think you need to think about adjusting your dog's levels of fat/protein/calcium/phosphorous etc. as it grows old - that's the beauty of a natural diet! I have a 13YO cattledog racing around the back yard here and she still gets the same raw diet she did 12 years ago. Her teeth are strong and white and she copes perfectly with anything I throw at her. Just like the younger terriers.
JMHO, of course!