Yes, sadly, I have to agree that it is an "old dude" thing, at least in gun culture. "Automatic" is mostly before my time. When I first got into guns, you heard some (older) guys say "automatic", but most of us younger guys just said "revolver" or "auto". In F2F conversation, at least with other intelligent people, I still refer to semi-autos as "autos" and they know what I mean. When I'm talking about fully automatic weapons, I usually specify "full-auto". So I definitely think there is a generational component. When writing I am more inclined to specify "semi-auto".
Antis and idiots of course, call everything "automatic".