And then I thought about it some more, and realized that my 25-year-old self, and probably even my 18-year-old self, would have immediately recognized that the guy was not a silly child who needed to grow up, but an absolute moron who would remain so for the rest of his life.
I don't mean that there aren't any things that one learns through age and experience - there certainly are, and some perfectly intelligent young people just haven't learned them yet, but it appears that the one thing that I unlearned with age is the ability to easily distinguish between immature and mind-bogglingly stupid. Should practice more.
(And to anyone else with whom I have argued last week: if you are reading this and know me in person, this is not about you.)