Archaeologists discover skeletal remains of humans in Ethiopia. Examination of the bone suggests that the remains represent four types of individuals. Two of the skeletons have bone densities that are 30% less than those of the other two skeletons. The skeletons with the lower bone mass also have broader front pelvic bones. Within the two groups defined by bone mass, smaller skeletons have bones with evidence of epiphyseal plates, but the larger skeletons have only a thin line where the epiphyseal plates should be. Give the age group and gender of the four individuals in this find.