Familial Mediterranean Fever (FMF) typically manifests between the ages of 5 and 15. However, the onset of the disease can occur much earlier, even in infancy, or significantly later in life. The attacks do not follow a regular pattern. They generally last between 12 and 72 hours, though they can extend for longer periods. While the frequency of attacks varies from once a year to twice a week, the most common occurrence is every 2 to 6 weeks.