Menstruation, also known as periods, typically begins during puberty, usually between the ages of 9 and 16. Most girls will start their periods around the age of 12 or 13, but it may be earlier or later for some individuals. The exact age when periods start varies among individuals due to factors like genetics, overall health, and lifestyle. If you have concerns or questions about when periods should start, it is always best to consult a healthcare professional.