First impression: why young men, but not young women?
They readily identify with their group. They form close bonds with its other members. They are prone to follow a strong leader.
This is a valid description of all people. I'm very wary of people putting gender in an issue that doesn't need to be gendered.
He seems to be making much stronger claims about the role of testosterone in behavior, aggression, and gender identity than any legitimate scientific claims I've seen about brain chemistry. Looking at the author, he has a vested interest in this: he's an emeritus (old) professor of neuroscience with a new book out about how testosterone is the root of human behavior. I don't think I trust him as much as I might if he was younger (more active in new, current research) and did not have a financial interest in writing this article. I don't know much of anything about brain chemistry or hormones, but I do know that they're complicated, and not to trust simple solutions or explanations.
We do know that young people are particularly susceptible to becoming fanatics, much like they are susceptible to joining cults, multi-level marketing schemes, or new age religions. I don't think you need to appeal to brain chemistry for that, though. Being young and having responsibilities, but no power, social standing or clear direction in life sucks. It's why people in my demographic are such easy targets for all of these schemes. People with financial security, three kids and a mortgage don't run off to join the circus, after all.
The stereotyped young man – loud, risky, unreasonable, aggressive (but also non-conformist and thus innovative) – might be one result.
Perhaps my experience is not typical, but I don't think I actually know anyone like this. And most of my friends are, like me, young adult males. Maybe we're all like this and it's easier to see from the outside? Maybe I don't like being put in a box so I'll just react negatively to any attempt that someone makes to do so, especially if it's unflattering? I don't think so. I can see the image of a scary young adult male painted by media, but it's an alien notion to me, and I think it's largely a myth. Young people are volatile, and maybe young males are scarier because of their perceived greater physical strength, but you lose out on a lot of understanding if you try to tie this all to masculinity, because some of the underlying causes are just about being young.
I see the utility in the tags #grrlski and #boyyski as being about the experience of being female or male in society, and the consequences of such. I do think this article is appropriate, as an example of the pressures and stereotypes on young men, as perceived by an old man with a book to sell. People are afraid that young men are fanatics, or that we're going to do something dangerous, because we're typically inexperienced and powerless, but also stronger and more idealistic. But that's just a mold that society wants us to fit in to, the mold of not fitting in,being aggressive, and making bad decisions. It really just is a stereotype.