What is a common complication associated with coitus at a young age?

The correct answer highlights the significant concern of increased risk of pregnancy associated with engaging in sexual activity at a young age. Young individuals may not fully understand or have access to adequate contraceptive methods, leading to a higher likelihood of unintended pregnancies. This risk can have profound implications for the health, education, and social circumstances of those involved.

While other options mention important health considerations, they do not directly relate to the immediate consequences of early sexual activity as closely as the risk of pregnancy does. Bone density issues, obesity, and emotional instability may be factors influenced by various lifestyle choices and biological changes but are not direct complications arising specifically from coitus at a young age.