I would seriously reach your natural potential before officially doing cycles. At age 21 and 165 lbs you still have about 40 lbs of muscle you can gain naturally. Train hard, eat big, stay disciplined, and want it more than anything and you'll become a 200 lbs beast without 500mg/test.
Then when you've reached that point you will start leveling off and progress will be hard to come by. That's when you make the decision to start doing cycles. So please hold off and start getting really serious about your diet and training. Max out first.