Many probably could swim -- given the right conditions, attire, and preparedness. Bobbing in the water, at night while dressed for dinner, I'm not sure.
I did the full clothing swim test at USAFA years ago. I would not want to try it now.
As close as they were, they could have back stroked it. It would have taken 5-10 minutes, even in clothing. The water was 57 degrees which is chilly but not fatal for that short of a time.
The elderly, however...