willem73: I actually know this for sure, because I'd measured my cock using a ruler on the back page of a field guide (birds, I think) I had (and still own). When I was twelve, I was 7.5" (I went though puberty a bit early, I think). I made measurements from all possible angles, and the weird thing is, the head of my penis didn't really grow much past then (my head's about 2.5" "long"). So, my penis lengthened and thickened, but the head size pretty much stayed the same.