See
here for a useful source of medical and other definitions. Here you will see that Impotence or erectile dysfunction is the inability to create or maintain an erection, despite sexual stimulation.
Male babies soon learn that playing with their willies is a source of pleasure along with many other erogenous stimulation. If by masturbation you mean an attempt to manipulate the genitals and erogenous zones with a view to achieving an orgasm, I think that boys do this just as soon as it either occurs to them or someone suggests that it is possible. Men continue to carry out this interesting experiment for so long as there is breath in the body, it seems.