Though the reference level of testo varies some what from lab to lab, here is a link from Mayo Clinic giving their standard levels up to adult age
. If you are within the range limits specified there for your age
then, you may need not have to worry, if not better to consult an Endocrinologist. Also, when you say penis growth, there is a large possible variation and individual perception can differ. So if you have any doubts, better to consult a urologist.