Familial Mediterranean Fever (FMF) typically begins between the ages of 5 and 15. However, the onset age can vary widely, from infancy to adulthood. While there is no specific regular pattern for attacks, they generally last between 12 and 72 hours, though this duration can be longer. Attack frequency varies from person to person, ranging from once a year to twice a week. The most common attack frequency is every 2 to 6 weeks.