Heat oil in a large stockpot over medium heat. Cook and stir celery, carrots, onion, and garlic in oil until slightly softened and fragrant, 5 minutes. Add turkey, bay leaves, salt, peppercorns, rosemary, and dried sage. Cook until fragrant, 5 minutes more. Pour enough water in to cover turkey and vegetables. Bring mixture to a boil, cover pot, and reduce heat to low. Simmer, skimming fat occasionally, until flavors are blended, 4 to 5 hours. Strain liquid into a container and discard carcass and vegetables.