How Long Does It Take For The Penis To Grow?

Im 17 and I believe that I have 7 inch by measuring the underside. Anyway, how long would I have left for this penis to continue grow? My physical height (5'7" or 5'8" maybe) is similiar as my four brothers. They are in their mid 20's and early 30's. Their puberty is over. Does this mean my physical and penis puberty is over? I have reached to my brothers' maximum growth.