If you are 13 and have a hard penis at 6.5 inches, you are big now and on your way to a good size when older, you are still developing for 3 or 4 more years. the average guy is between 5 and 6.25 inches, so since you are still growing you already have most guys beat, good for you.
i personally measured myself, coz im NORMAL.
(And cuz my mom wont let m touch her sewing ruler)