“I hate the 'old people don't understand' line. Of course they understand, people don't suddenly become stupid because they are old.”
Whilst this is true, it's also true to say that this is the age group where you are more likely to see onset of deterioration of brain function. It's possible that some of these older people are not quite grasping the situation as well as they might ten or more years earlier, in addition to possibly feeling that they'll take their chances as they've had their "three score and ten".
I wouldn't say that they are the only ones to be going out more often than they need to though, it's definitely unfair to say that. Where I live there is a widespread range of ages going out and pretty much all of them (that I have seen) have given other people a wide berth, regardless of the age group. I do think if you are sensible when you go out, and follow sensible rules - avoiding touching things unnecessarily, avoiding sneezing/coughing into the atmosphere, using hand sanitizer and washing your hands - then you are unlikely to do harm.
Having said that, I do think that if people when going out went by the premise that they should behave as though they are infected, rather than behaving like they know they're not, we'd reduce the rate of spread far more effectively.
But there are always people who refuse to comply and go their own way, regardless of what they've been told. It was the same during the Bubonic Plague of 1665, it's the same now, it will be the same next time. People are people and don't change.