Yes, an appendectomy isn't a particularly complicated surgery to perform and could have been done far earlier than the 1300s. Galen and Celsus both discuss the management of penetrating abdominal injuries including repair of intestinal lacerations and layered closure of the peritoneum, abdominal muscles, and skin. The difficult part for the 1300s surgeon would be management of complications like infection, which would have been difficult or impossible without antibiotics, and more likely than today in an era before modern antiseptics and sterile surgical gloves.