People think it’s so obvious the shooters are young men that there’s literally no point in saying so. In that sense, ‘gunman’ is internally redundant; everyone knows that ‘man’ follows ‘gun.’ 

As long as men, young and old, have easy access to high-capacity killing machines at the same time their society furnishes them with endless heroic masculine narratives about redemptive violence, the next tragedy is always going to be just around the corner.