What's really worrying is the juvenile tastes of so-called grown-ups. Being addicted to video games well into one's 20s and 30s (and before long, 40s). Creating a mass market for blockbuster movies based on kid's toys and cartoons. They made a Transformers movie when I was little, but it wasn't marketed to everyone. Even I didn't see it, and I was part of the small target audience. Listening to pop music that is so drained of emotion it sounds like they haven't even gone through puberty yet. And on and on...
If the main driver behind changes in the zeitgeist is whether the violence rate is rising or falling, we should expect to see something qualitatively similar from the mid-1930s through the late '50s, another falling-crime period. Since most of that time has faded from memory, we have to turn to historians of popular culture, as well as look into things on our own.
John Springhall's book Youth, Popular Culture and Moral Panics: Penny Gaffs to Gangsta-Rap, 1830-1996 details the elite outrage over penny gaffs and penny dreadfuls in Victorian England, gangster movies and horror comic books mostly in mid-century America, and gangsta rap during the '90s. For that decade he should have included the violent video game panic, which gave rise to the ESRB rating system. Not surprisingly these are all from falling-crime eras, when moral reformers act more like thought police and media censors, whereas in rising-crime eras they act to keep out poisonous physical substances like drugs. (That's another topic, which I'll get around to sometime.)
For now, let's stick to the mid-century period and comic books. Although there were a few, admittedly very popular, superheroes introduced through comic books in the 1930s, like Batman and Superman, by the '40s that trend died off and would not be revived until the '60s. During the '40s and '50s, comic books moved more toward the genres of horror, crime, Westerns, romance, etc.
Relying only on others' descriptions, the Western genre sounds like simplistic war movies like 300, and the romance genre like your standard chick lit. The covers and content of horror comics are strikingly similar to the recent "torture porn" in movies and video games. The crime genre sounds and looks more like the Law & Order TV show, especially its lurid spin-off Special Victims Unit. There were entire series of crime/gangster comic books from the '40s and '50s that focused just on women criminals. And they peddled exactly the same fierce-minded butt-kicking babes and GIRL FIGHTS! that provide shower-nozzle masturbation material for today's emotionally stunted and feminized nerd audiences. (See here for a great gallery of crime comic covers.)
Were comic books back then just kids' stuff? Not at all (p. 129-30):
An American survey of 1950 revealed that there was indeed a large adult readership for comic books, horror and otherwise. Roughly 41 per cent of adult males and 28 per cent of adult females read comic books regularly. In the same year a government-sponsored survey of an Ohio town found that 54 per cent of all comic book readers were over 20 years of age. These percentages are placed in perspective by the 95 per cent of boys and 91 per cent of girls between six and 11 who read comic books, while 80 per cent of all American 'teenagers'... read comic books as well, usually a dozen or more every month in the 1950s.
Thankfully they weren't as common among adults as among children, but it still should have been about 0% of grown-ups who read goofy immature junk like that. I'm not slamming popular vs. elite entertainment, but the specifically juvenile aspect of it all.
I wish I knew more about the history of radio dramas, since that was another huge form of popular entertainment that we don't remember anything about by now.
As for popular music, I'm not going to rate every top song for how childish it is, since that's a bit subjective. It's easier to find hit songs that are clearly kiddie stuff, and to treat them as the tip of the iceberg (or the tail of a distribution). Here are just those that reached #1 on the Billboard charts:
1948 "Woody Wood-Pecker"
1949 "All I Want for Christmas (Is My Two Front Teeth)"
1950 "Rudolph the Red-Nosed Reindeer"
1953 "(How Much Is) That Doggie in the Window?"
1958 "The Purple People Eater"
1958-9 "The Chipmunk Song (Christmas Don't Be Late)"
Remember, this isn't a list of songs that were played on the radio at all, but those that topped the charts, and not for a children's category but for pop music overall. Some of those are likeable enough for adults to listen to them, although not so great that they should reach #1. And others can't even say that -- even as a child I couldn't stand that annoying doggie in the window song. I heard more grown-up music in the theme songs to my cartoons.
When the crime rate started rising in 1959, people wanted to grow up sooner, so this trend gradually died off. In 1962 "Monster Mash" hit #1, although at least that one was about parties and dancing. The last major entry was "Hello Muddah, Hello Fadduh", which reached #2 in 1963. After that, when "Sixties music" proper began, you didn't hear any of that stuff. At least not until 1997, when "Teletubbies say 'Eh-oh!'" topped the UK Singles chart.
Obviously other factors contribute to grown men acting like 10 year-olds, like living at home into their 20s, not having to earn their keep even if they do move out and get a job, working in a more feminizing service as opposed to a manufacturing economy, and so on.
Still, the influence of the rising vs. falling crime trend is strong enough that you can see a lot of today's man-children culture thriving in the mainstream during the '40s and '50s. Particularly compared to the Jazz Age before and Rock and New Wave Age after, the relative immaturity of the mid-century period jumps out. Movies like Double Indemnity, Sunset Boulevard, and Rear Window really were exceptional, the refugia of a cultural ice age.