Funny thing is, I had a nice conversation with one of these guys earlier, talking about handloading for 30.06.
That makes me think that it was not purely discrimination due to age, or you wouldn't have had the opportunity to have a nice conversation in the first place.
When the handguns came out the attitude changed.
I can't get a clear picture of how exactly your friends were shooting. But, perhaps it was not specifically the shooting of the "highcap" handguns itself but the general demeanor they portrayed while shooting the handguns. Maybe yelling "f--- yeah! or "woohoo-ing" or appearing in some way unruly to their eyes? I don't know, you tell me, but I can say that usually anything even remotely hinting towards the potential of horseplay will get on peoples nerves at a shooting range, even if no horseplay actually occurs.