This study aimed to present the menarcheal ages of girls from different families, backgrounds, and social strata with respect to their BMI. This study included 119 girls (aged 16–19 years) from Polish sports schools. Using a diagnostic questionnaire, data on the girls’ age at menarche, their living environment, parents’ education and occupation, social origin, and others were collected. The body height and mass of the girls were measured, and the Body Mass Index was calculated. The significance of the differences was assessed using ANOVA, Fisher’s least significant difference test, and t-test. Spearman’s rank correlation coefficient was calculated and the analysis of correspondence was made between the age of menarche and the ranked variables. In conclusion, the average age of menarche among the studied samples did not significantly differ from that in the population living in western Poland. Girls from locations with 100,000 or more inhabitants and whose parents have higher or secondary comprehensive education are early maturing, whereas those from smaller towns and villages and whose parents only have primary education are late maturing. Girls with overweight or obesity mature earlier than normal and underweight girls.