In a large deep skillet brown the sausage until cooked through. Add the onions and garlic and cook until onion is transparent. If the sausage is very lean, you will need to add 1-2 tbsp of butter. Sprinkle the gluten free flour over the sausage mixture. Stir until well blended and cook about 1 minute. Pour in one cup of the milk and stir well to avoid lumps. Keep adding the milk in 1 cup increments, waiting 1 or 2 minutes between additions, until gravy is desired consistency. Add the sage, paprika, and salt and pepper to taste. If you simmer the gravy longer it will get very thick, so you may need to add more milk.