Fish oil is a commonly consumed dietary supplement as it is widely used to promote heart health, battle inflammation, and remind the brain's function under it. For a 15-year-old, the recommended maximum amount a day would range from 500 mg to 1000 mg. Try taking the tablets with food to enhance the absorption process. Be cautious that you only select those supplements that have high quality to ensure that you are experiencing the best advantages of the supplement. If you have any specific health problems or health conditions, you should consult with your physician.