Like all changes related to hormones and puberty, menstruation can start at a different time for every girl. Some girls move through puberty faster than others, and some simply start a little later. Moreover, girls get their first period around 2 years after displaying the first few signs of puberty. Some girls may not get their period till after they are 16 and some may get them as early as 9. It can be different for everyone and it's normal.