How can a16 yo broaden hisshoulders?

Shoulder: You cannot broaden your shoulder/collar bone once your bone stop growing. Your are16 yo, so is possible you may still be growing (your doctor may order xray to determine if you are still growintg. You can increase your muscle size (not total number of cells) on the deltoid, trapezius, and other neck/chest muscle with diligent weight lifting, nutrition, and time.