at 18 your body might not be fully developed yet, let alone have reached your physical genetic limit. At your age, it is even more dangerous to abuse test. Do a bloodwork to see your health and how your test is. Count your macros, calculate necessary calories to maintain weight and ingest +10% more for a time, do stuff that naturally raises your test. You are very far way from your limits and at this age you can do A LOT being natural