Scientifically at age 16, unless you’re tecsan or bjuk, in which it starts developing at 40.

Well, by the looks of some members here, I would say… the penis stops growing at age two years old

Sorry, i think a normal cock quits developing about age 16 or 18. Mine was full size at 12 or 13. Although the base of the shaft continued to get bigger with use.

mine was about 13 or 15 years

15-16 aprx id say. At 20 it's definitely done growing in my opinion.

I’m not sure about other guys but I can tell you that when I was just about 13 years old my cock was much bigger than the other boys. I measured 7 1/4 inches long and 5 3/4 inches in circumference. I used to be able to suck on my own cock. It has always measured the same size. It’s just thicker in circumference these days

I don't know at what age it reaches full size but I can tell you that it reaches it's limits quite frequently.