Exactly, at your age your body produces enough test so that 200mg wont do shit, it ll just turn your own production off and replCe it which is stupid.
And your doctor is an idiot for couple of reasons:
1. Prescribing test to 22 year old for sole purpose of cycling
2. Telling you to "taper down" test

Bottom line is, Don't use it and stick to training naturally till you are older. Don't worry about your test it wont go bad for another couple of years