Most of us survive to tell our tales of derring-do, or to be roasted at 21^st birthday parties for our death-defying rites of passage.

Carl Salomon and Tolga Toksoz will not reach that milestone. Both were 19 when they died in Sydney in recent days while taking big, though by no means extraordinary, risks.

Salomon, a Sydney University student, plunged from a 30-metre crane to his death in Sydney Harbour about 5.15am on Thursday last week. He had been swimming with a mate and police suggested "skylarking with alcohol involved" caused his death.

Two days later, Toksoz was at an all-night dance party, A State of Trance, with his brother and friends at Sydney Olympic Park. On the account of assistant Police Commissioner Frank Mennilli, they played an "idiotic" and lethal game: who could pop the most ecstasy pills? If Toksoz won, he also lost.

Then, on Monday, a 29-year-old German tourist rode his skateboard down the steep and winding Moss Vale Road on Barrengarry Mountain in Kangaroo Valley. It is likely he had watched YouTube videos of swarms of thrill-seeking skaters negotiating the same blind bends and dodging cars climbing the hill. This tourist did not dodge death, however. He fell into the path of a truck.

Coroners will consider the horrifying details. In the meantime, the proximity of these tragedies might give pause to young people – especially males – who put themselves at regular risk.

Males aged 15 to 24 are more than twice as likely as young females to end up in hospital, the Australian Institute of Health and Welfare reported last year. They are more than twice as likely to die or be injured in road accidents. While more than one in 10 young women experienced some form of violence in 2012, the figure was almost one in four for young males, the Australian Bureau of Statistics reported.

It is a similar story globally. Young males account for 75 per cent of fatal injuries in the 15-24 age group in the European Union.

"There is a faster maturation of the frontal lobe in girls," explains psychiatrist Ian Hickie, executive director of the Brain and Mind Research Institute at the University of Sydney. "That's the part of the brain that says, 'No, it's a really dumb thing to do'."

From puberty, both boys and girls take greater risks. They become sensation seekers. Changes to the brain's "socio-emotional system" lead to increased reward-seeking, especially when among peers. This has been a focus of research by Steinberg, professor of psychology at Temple University in Philadelphia and author of Age of Opportunity: Lessons From the New Science of Adolescence.

That new science, including brain imaging, has revealed "adolescence" – from a neurological view – can continue well into the 20s, especially for males. Guidelines for British psychologists now extend the definition to 25. Australian adolescent psychologist Darryl Cross argues it could be as old as 28, while Hickie believes most male brains mature to adulthood at 21 or 22. For females, he says, it is 19 or 20.

Still, this challenges the common view of adolescence. "We have this notion that you're a child until you're suddenly an adult on your 18^th birthday," Hickie says. "And you suddenly move from immature decision-making and recklessness to maturity and consideration.

"In the past, ironically, we didn't think it was such a good idea - under the age of 21 - to get married, to trade property, to drink alcohol, to vote, to go to war. But then, particularly in the 1970s, we decided people should be free to make these decisions at much younger ages … It turns out the old way of thinking was more in tune with what we now know about brain science."

The biological discoveries aside, however, Hickie worries about a phenomenon of our own making - what he calls the "social prolongation of adolescence".

Previous generations had commonly left school at 15 or 16, took jobs among older workmates and soon established their own homes and life-long relationships. "The danger now is that we're extending high school into the early 20s: living at home, partying, prolonging our years among immature peers, and recording it all on Instagram or YouTube while taking no responsibility and not interacting with socially mature organisations.

"The longer you sit at home funded by your parents, living as if you're 16, the longer you will tend to behave like that. It's a really serious developmental issue."

Mennilli was clearly moved by the death of Toksoz and the ecstasy "game".

"Look, shocking isn't the word; idiotic is the word," he said. "These people were gambling with their life."

Since then, parents have been asking Paul Dillon, who runs Drug and Alcohol Research and Training Australia, if there is a new fad – young people competing, in the manner of a drinking game, to swallow the most ecstasy. Dillon sees no evidence that this is prevalent, and he fears that any misinformation about "the dumb things kids do" will only make them more cynical.

"They don't believe anything we tell them about the dangers of ecstasy," he says. They commonly double and triple their doses to intensify the effect.

But ecstasy may be an exception, Dillon says. More generally he agrees with Steinberg, who argues that adolescents are equally as aware as their parents of the dangers associated with risk-taking. Steinberg cites studies that show their risky behaviour does not stem from ignorance, irrationality or delusions of invulnerability.

They are well educated about the dangers but, while their frontal lobes await maturation, they proceed to take the risks.

"Attempts to deter risk-taking through education are not very effective," Steinberg tells Fairfax Media, "because once they are in the moment, adolescents tend not to pay attention to what they've been taught. I would think that in the abstract the fellow who swallowed the ecstasy knew this was dangerous, but in the midst of a party and contest, this knowledge wasn't very salient.

"I've suggested that we try to reduce risk taking by trying to change the context rather than the kid. In these instances this would mean making ecstasy harder to get, making the crane more secure against trespassers, and patrolling the [skateboarders'] hill more vigilantly. Obviously one will not be 100 per cent successful in any of these, but any success will save lives."