Just saw this. I'm in the UK belong to a gym now that has quite a lot of older folks. Strangely enough I have NEVER seen old people behaving as described. They are usually among the most courteous.
In gyms all over the world - US, UK, Japan, France - I've usually found that the worst "displayers of junk" are the ones in their 30s to 50s who maybe used to be strong, are now turning fat, and are generally trying to act like hard bastards. It's basically the same guys who drop the barbells, don't put the plates away, occasionally do a lift with too much weight and 1/4 of the normal range of movement and grunt loudly. It's an attempt at some sort of male dominance show, kind of like baboons.
Worst offenders were the Yakuza wannabes in the national stadium gym in Tokyo. Japanese gyms have a big communal bath which allow great opportunities for "exhibitionism".
If you outnumber them, the best way to handle it is to point and comment noisily - "Yuk, look at those wrinkly old balls!"