I'm linking this news report because I didn't think it was possible to increase penis size after puberty. I know none of you will be happy with the protocol they used.
Due to a lack of the male hormone, the unnamed patient had just a 5cm-long (two inches) member at full stretch - equivalent to a 12-year-old. But after doctors corrected the 34-year-old's lack of testosterone, they were able to expand it to 9.1cm - dubbed the average size.
The man was between the normal ranges for all hormones except testosterone, which he severely lacked. He was found to have 55.99 ng/dL of the male hormone. A treatment course of nine months of testosterone replacement therapy was then recommended to him. He went ahead with it, and was given an injection of 250mg once every four weeks to help boost his count of the hormone. This later decreased to once every six weeks when the treatment, which the doctors said can impair a man's fertility, was starting to work. At the end of treatment, his testosterone count had increased to 433.8 ng/dL and his penis size had doubled. The size of his testicles had also doubled, with them having just a 10ml volume - the equivalent of a teenage boy, before he started the injections.