Which of the following is NOT a risk factor for gallstone formation?

Gallstone formation is influenced by a variety of factors, with obesity, high-fat diets, and smoking being well-documented risk factors. Obesity increases bile cholesterol saturation and the formation of stones. A high-fat diet can lead to elevated cholesterol levels in bile, which predisposes to stone formation. Smoking has been linked to many health issues, including an increased risk of gallbladder disease and possibly influencing gallstone formation through its effects on metabolism.

In contrast, while age can play a role in the overall risk for many health conditions, including gallstones, simply being in one’s 60s does not directly influence the biochemical mechanisms that lead to gallstone formation in the same consistent manner as obesity, dietary habits, or smoking. Thus, age alone does not accurately represent a direct risk factor for the development of gallstones, making it the correct answer to identify as NOT a risk factor.