I'm not sure if its good for ALL ages but I know @Gertie's Mom has been her pups canned pumpkin for a while and they are puppies (use pure pumpkin not the pie filling). For my Samson I just give him a heaping spoon full, I don't measure it actually. I'm sure everyday is ok but I am confident to say that every other day is definitely fine.
Well that all depends on what his allergies are. I have to be grain free and I try to avoid chicken with him so I have limited options myself.