Well, this is quite a thread ! Let's see... first of all, 1987, September, Black Sea seaside. I was 8 and I remember me noticing that my pee-wee was filling more the swimming-suite I wore when comparing with other guys (ah, the old-fashioned Communist designs for such clothes... pooh !).
In 1989, during a summer holiday a friend of mine showed me "a secret". He said he knew "what do older guys do with their cocks." "Huh ?" And he wanked (jerked) a bit, his flaccid penis gaining some size. When I did that, I discovered that my schlong was bigger, both length and width. But well, I ignored it.

The first time I measured my penis... Summer 1992, aged 13. Someone whose cock was reaching 12 (4.7-inch) cm fully erect (he was very happy to be "resting on the laurels of his virility") challenged me. To his surprise, I was 15 cm erect (5.9-inch). I couldn't truly care less; after all, a cock was a hidden stuff, nobody sees it so it's useless to compare 2 cocks simply because it's not a pride that you make public. And there he goes, Ralexx... when I met the same guy a year later, it was something else. Porn magazines were now available, xxx films were broadcast after midnight, boys were talking in the classroom, and penis size emerged as a topic, à la mode among teenagers (classmates). So, when I met again this guy (July 1994), M., he was 14 cm long, I was 16.5 (6.3) and we said we'll keep comparing our dicks to see if we're "men enough". In January 1995 he was still 14 cm, I was 17.5 cm (a bit under 7) - and, geez, he was 1 year older than me. Now drama occurred : I had the same size while he grew from 14 to 16 cm (May 1996), though less thicker. He was too damn close. "Ok, then..." and Ralexx searched for consolation in ignoring his size for a long time : 2 and a half years. M. moved from the town, so there was no chap to talk about penis size with. No ruler, no tape measurer, just the joy of feeling it thick and heavy and quite big.

New Years Eve came (1998/1999) and M. paid me a visit. Of course we ended with our pants down and fully erect. "OMG !" were his words. What was the problem ? He was 16, I was 19.5 (7.8-inch), but heftier; it really looked massive compared to his. (Don't ask what did he do next... you guessed, I bet... yep, the fel-- word). Another period of disinterest towards penis size issue came to me...
July 2002. I felt something was different, because when peeing I the flaccid size seemed bigger to me. Took the tape and measured again. 21.3 cm = 8.4-inch.
I stated 8.6 for LPSG (last measured December 2001), but it happens that I feel it's bigger, when having sex, around 9, maybe more, maybe less. But I don't jump from bed to grab the ruler, it would be at least childish. I simply have the intuition it will grow more. (Even though I'm almost 23/24 yo.)