You probably wont get a lot of advice from the experienced members here because we dont advocate taking gear at 18 years old. At your age, height and weight there is plenty of room to gain muscle naturally. Steroids wont make you cut down to 6-7% bf. Diet and cardio will. If you plan on taking just test, your results will be shit because you're trying to cut. During a test cycle you need to eat like a horse to get good gains, not employ a cutting diet.