A male’s penis has reached maturity by the time he reaches his 17th birthday. The average size of the adult penis for men 17 and over is 6 1/4 inches.
Although a man can reach maturity at an earlier or later age, it is unlikely that it is still occurring at 21.
July 28, 2009 | 
Author 
Posted in 
Tags: 
It varies for a lot of men, although there is some evidence of a few men getting it about 21 or so
A male’s penis has reached maturity by the time he reaches his 17th birthday. The average size of the adult penis for men 17 and over is 6 1/4 inches.
Although a man can reach maturity at an earlier or later age, it is unlikely that it is still occurring at 21.
HA I DON’T KNOW