I think that the trend actually hits both ends of the knowledge spectrum, regardless of age. Dunning-Kruger will make those who know little honestly believe that they know everything worth knowing, whether they are a kid who hasn’t had time to learn or an older person who lacks the mental flexibility to learn but refuses to admit that and thus blames the world for being too full of “stuff not worth knowing”. Conversely, those who actually know a lot tend to be just as egotistical, the difference being that they can back their claims of superiority with actual competence.
You see this a lot in competitive areas like sports or certain genres of online gaming, though the latter often extend their superiority at that game to imply superiority in all aspects of existence. Watch a football player run the ball into the end zone; quite a few of them will ditch all humility and (in the NFL) risk a penalty for “excessive celebration” because their egos just won’t let them not taunt those who they just “proved” to be inferior.
And since American society is highly competitive to the point where nearly everything is about winners and losers, you’ll see the same behavior in everyday life here that you’ll see in online shooter games. Those who excel at the game, whether literal (online shooters) or metaphorical (how wealthy/influential one is), will mirror the behavior of older folks by dismissing the opinions of those who disagree with them, while those who suck at the game will mirror youth by claiming they are perfect and the game/world is flawed, and everyone else is at fault. (Okay, maybe not “mirror” since they tend to be under 20 anyways and are just acting their age while most of the players who are actually good tend to be in the 28–35 age group, but you get the point.)
In short, it’s not a matter of age, but of ego, and those over-50 are FAR from immune to having the same flaw.