Gwen started her menstrual period about two years earlier than magda, even though both girls are very healthy. a likely explanation for this event is that

Menarche is the name of the first menstrual cycle experienced by a girl. It can take place between 12 and 16 years old. Genetic, sociocultural and specially nutritional conditions affect its timing.

For instance, weight is highly influential. In girls with a low body mass index (BMI), the body saves energy for other more vital processes and menarche and menstruation appear at an older age. Hence, the difference in weight could be a natural factor that explains why Gwen started her menstrual periods earlier that Magda. Magda's BMI should be lower. Another common factor which delays menarche is sports. A girl who has a demanding sports life usually experiences her period later. It could be also a possiblity that Magda is a sports girl and Gwen is not.

But the correct biolycal development of a woman's body is usually not affected by the age at which the menarche takes place. Nothing is necessarily bad in a woman's body because of experiencing it later.