Some boys start puberty around 9 and others don't start until they are Usually by the end of puberty, a guy's penis has reached its expected size. Puberty.
Learn about the stages of puberty and find out the average penis size of boys 10 to 18 to determine whether or not you should be concerned.
First the penis grows in length, then in width. Teenage males seem to spend an No contest: size. See Concerns Boys Have About Puberty.