Little boys seem to cry a lot but then magically men stop crying.
How is this? Is there like some lever in the mind that gets triggered at age 12 to stop the crying?
I dont get it.
I have honestly never seen little boys cry much aside from the occasional outlier. That may not be true today as I don’t see little kids that much anymore.
In essence, yes. That “lever” is called “society”/“peer pressure”. In our society, it is acceptable for young boys to cry. But there is this implied, macho, “real men don’t cry” attitude in our society, such that this acceptance wanes for boys as they reach puberty (depending on the parents, sometimes even before). Typically (sadly) this change in acceptance is taught via…ridicule and humiliation.
When you’re a grown-ass adult you’ve (hopefully) developed better coping mechanisms. I never got “peer pressured” into being “macho”, I just figured out over time that crying isn’t helpful. When you’re a kid, every shitty thing that happens is the end of the world, then you live through it and realize maybe it wasn’t that bad.
My son is four. He started crying last summer because he filled his little plastic wagon too full of cucumbers from the garden and it was too heavy for him to move. Hopefully he doesn’t cry about things like that when he’s forty. It’s a bad look.
I don’t remember crying as a kid, and I don’t cry now.
How well do you remember before you were 5? I think a lot of boys start trying not to cry around that age (though mine, at 5, is still a crier–but he hasn’t started Kindergarten.
Most women also don’t cry anywhere near as much as when they were 3yo. Are there exceptions? Sure, but I know men who cry like Magdalenes too.
I’m not sure what subtle aspect of this question I’m missing. Surely relatively helpless infants cry in order to petition for attention and assistance from their parents or other caregivers. Past childhood, people are expected to be able to fend for themselves to a much greater degree, or when in difficulty to use words (or in extremis shouts or screams) to elicit the specific assistance that they may need from those around them.
Cultural expectations. I tended to cry into my teens. After been tagged with a bunch of derogatory nicknames and teasing, I learned to suppress the urge.
Note that, at one time, tears were considered a sign that you were “manly” (See #4.). That would indicate it’s all peer pressure.
You also cry less as you learn to manipulate your environment. As a baby, it’s the only way to express your needs. As you get older, there are other methods.
From your link, apparently
It’s a little hyperbolic to conclude from this that tears were once a general sign of manliness.
I have clear memories of my driving test at 16. 
Nothing prior to five.
Women also cry less than girls. Perhaps not by the same margin, but noticably so.
Puberty?
You’ve never heard a parent/adult tell a little boy “big boys don’t cry”? It’s pretty standard and IMO not at all ok.
My father preferred “stop your crying or I’ll give you something to cry about”
We learned it from 10CC.
Sent from my adequate mobile device using Tapatalk.
Culture and hormones. That’s it!
Crying isn’t just about shitty things happening to you (the crier). It’s also a response to sad situations, such as movies, news segments, or the suffering of loved ones. As noted upthread, for cultural reasons it’s a response that many men (including me) feel uncomfortable exhibiting. Sometimes I’m able to suppress it, but on occasions when I can’t, I find it highly embarrassing; I don’t want the attention it inevitably draws.
A perfect answer 
“It’s just a silly phase… I’m going through.”
But more complicated is that there’s not much worth crying about. Now that I have a world of perspective, I understand that my skint-up knee or the flat tire on my car just isn’t worth crying about. I mean, it doesn’t upset me to that point. It’s all in the perspective, my good man/woman.
Now when my ol’ hound, Duncan, leaves this planet, oh, you’ll see a grown man cry then.
Childish crying often comes from frustration. Men control their emotions as they grow older if they want to be well regarded by their peers and there are other ways to expresses frustration if you cannot hold it in like cursing and yelling.
There are obviously times men cry but generally unless it’s an emotional nuke as you grow out of childhood you simply aren’t swamped with emotion as much as when you were a kid.
… cursing and yelling are better ways to express frustration because why?