I take it no-one here has heard of the Arabic exercise known as "Jelqing"
basically fathers would take their sons to the Arabic equivalent of the physiotherapist, who would therapeutically stretch and exercise the boy's penis. They believed in it, no idea if any clinical studies have been done (probably not). I assume the jelqer would have historically been a eunuch slave.
It seems to have become "a thing" to be discussed in lifestyle mags such as Cosmopolitan and GQ (aka Gay Queens). Whether it would work on a adult is highly unlikely I would have thought
there are plenty articles on the web, this is one example
External Link/Members Only