When I was 7 or 8, I was probably about 2.5-3 inches.
By 12 I was probably still under 4 inches.
But at 14, when my cousin and I read the "what's happening to my body book for boys" and decided to try to have this thing called an "orgasm," he said he couldn't believe how huge my dick was. We got a ruler and I was almost 6.5 inches. I had had quite a growth spurt that was surprising to myself once it was measured. (He was 13 and smallish, and barely grew to 5 inches by the time he was 17 and we quit masturbating together. He confided to me once that he's still small and wishes he had a big dick like mine.)
Although I never really charted my progress anywhere, I've always played with myself and have always been very fascinated by my erections. (BTW, my erection has ALWAYS been the same shape--only the size has changed. My erection is straight side to side, but with a banana-curve downward starting 1/4th of the way out.) It's a shame I didn't learn what an orgasm was until I was 14. I did shoot a nice white load with my first orgasm though; that was a nice, pleasurable surprise, because I figured, from the book, that nothing would come out my first few times.
I think my penis quit growing at about 22 years old, at it's current approximate length of 7.5-7.75 inches. I'd never measured circumference until a few years ago, but it's 5.5 inches--not particularly thick for this place, but I've been repeatedly reassured that it's more than enough. (So lets call me 7.5 X 5.5 today. I hope that's big enough for this place.)