Other than elderly drivers (like you mentioned) I'm not sure I can narrow it down to one subset of drivers, but I can tell you that drivers in Central Florida (where I live) seem to be much worse drivers than in other parts of Florida. Don't understand it, but there it is.
People who talk on cell phones while driving tend to drive shoddily - my nephew is having to have his face rebuilt right now because he was driving and talking on the phone - so BEWARE!
....well, I wasn't going to say this but what the hell...I really hate to say it because I am a woman...but I find that women are very often, and this is just from
my own experience and observation, much more aggressive and reckless on the road. What's more they are most often rude and inconsiderate. Of course, there are exceptions and there are many men on the road who drive like idiots, but when I see something that makes me go "wha?" and get close enough to see the driver, MOST of the time it is a woman. Gotta call it like I see it.
Of course,
I am a courteous and excellent driver.