Wow, thats a lot of incredible milestones. I have vibrant memories of my milestones as well although they aren't much like all of the well endowed guys here. While I got to see many of my friends from a very young age, I will stick to my memories of just one of them in comparison to mine as they are burnt into my memory like no others.

Age 10: saw my 8 yo friend with a hardon for the first time and was absolutely amazed at how much larger it was than mine. I would have been too embarrased to let him see mine at the time. It was a bad milestone for me for sure.

Age 12: same friend, who was now 10yo asked me if I ever beat-off. Then he went on to show me his hardon which again absolutely amazed me because it was so much bigger than mine. Again there was no way in hell I was going let him see mine and know that mine was so much smaller. Another bad milestone for me.

Age 14: same friend who was now 12yo asked if I had any pubes yet. I said yes and he said that he did too and said he would prove it if I showed mine first. I showed him only my full bush of hair (not my dick) and he then showed his hairless dick. This was an awesome milestone for me because his didn't look way bigger than mine anymore. I didn't have any idea that mine had even grown at all. Later that same night I got brave and let him see my dick for the first time. We both were hard and as far as I could tell, we were about the same size. My first good milestone.

Age 15: friend was now 13 and kept asking to see my dick. I kept telling him that it looked the same as the last time he saw it. When I did show it to him, he said my dick was huge. When he showed me his, my first thought was that his must have shrunk. It appeared so small to me that I could hardly believe that, just 3 years prior, I thought his dick was huge. I was so naive that, until that moment, I did not realize that my dick had still been growing. My second good milestone.

No milestone here but, after the experience above, we started having mutual jack-off sessions so I saw my younger friend and his small endowment on a somewhat regular basis.

Age 16.5: we had not had a mutual jo session in about a month and my now 14.5yo friend claimed that his dick had been growing. Before revealing ourselves to each other, he bet me that his was within a half-inch of the length of mine. It was going to be the easiest $10 I ever made. I won the bet but it was just barely over a half inch difference so I didn't make him pay. This was another definite milestone although it was a bad milestone in my mind.

Got together about once a month for the next 3 to 4 months and his was obviously growing closer to the size of mine each time. He was still pubeless and I still had him beat though.

Age 17: 2 or 3 months had passed since we had last jacked together and my curiosity was killing me. After school one day I saw him getting on the bus and jumped on the bus behind and started calling him a little freshman. By the time we got off the bus at our street, I had given him enough trouble that he was ready to show me that I was a little junior. We got to my house and both stripped down to compare. For the first time, he had just a few, barely visible pubes. He was still such a small boy that he had to stand on a stepstool just so we could compare them side by side. He just edged me out although I really thought his looked very large compared to mine. That was my last milestone. Another bad one unfortunately.