Mix sage, salt, black pepper, red pepper flakes, and marjoram together in a small bowl. Place turkey into a large bowl and mix in spice mixture with your hands until well combined. Form into 10 patties. Cook patties in batches in a large skillet over medium-high heat until no longer pink in the center and the juices run clear, about 5 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).