Several years ago, a plastic figurine began appearing around Google's offices - an ageing alien with grey hair, a Google Glass headset and a sign that read, "Get Off My Lawn!" The doll, a special edition of Google's Android mascot, was a jokey tribute to the "Greyglers", a group for the 40-and-over crowd at Google, and the doll hinted at how it felt to be an older worker in tech: funny, self-conscious, a little out of place.

The Greyglers still exist, but they're no longer such an anomaly. Sundar Pichai, Google's 45-year-old chief executive, would fit in the group. So would Larry Page and Sergey Brin, who co-founded the search engine as graduate students two decades ago; Susan Wojcicki, an early employee who runs YouTube; and most of the company's other high-ranking executives.

For years, the self-appointed leaders of Silicon Valley were young people - mostly men - with age-appropriate behaviour. They adopted brash mottos like "move fast and break things" and eschewed work-life balance in favour of all-night hacking sessions in offices that looked more like college dorms. Their successes were cheered, and their sins were shrugged off as the cost of innovation.

"Young people are just smarter," Mark Zuckerberg crowed back in 2007, when he was the 22-year-old wunderkind behind a fledgling social network.

Now, of course, Facebook is a global powerhouse, and the company's pursuit of growth at all costs has led to some truly dire consequences around the world and fuelled a larger backlash against tech.

At the same time, Mr Zuckerberg has disproved his own theory. Now 33, he is still not old by any measure (except perhaps his own). But he is a smarter and more self-aware leader than he was a decade ago, and he has shown more willingness to accept responsibility for the company's mistakes.

After years of moving fast and breaking things, Facebook is at least acknowledging its flaws and trying, albeit clumsily, to fix them. That's a start.

There's a lot of growing up happening in today's tech industry, where former whiz kids made their fortunes and are now settling down, starting families and starting to think about their legacies. Tech's workforce remains young - according to PayScale, the median employee at the five largest tech companies is around 30, roughly a decade younger than the median American worker - but the industry's leaders have gotten older, and are seemingly more attuned to the power they wield.

"Five years ago, there was no talk of empathy or moral responsibility," said Om Malik, a venture capitalist who has written about the tech industry for years.

Certain corners of the startup world, such as cryptocurrency ventures, are still filled with reckless renegades. But the industry's largest companies are now mature, bureaucratic businesses whose daily decisions are heavily scrutinised. That's a good thing, since the issues many of these companies face - global information wars, regulation and privacy concerns, diversity and sexual harassment challenges, and worries about technology's effects on billions of people's brains - will require thoughtful, grown-up solutions.

In recent weeks, I spoke to numerous industry insiders about this coming of age. Here's what I learnt.

Tech leaders are becoming more realistic and introspective. Gregor Hochmuth, 33, an early engineer at Instagram, said some of today's Internet giants had grown up with positive-thinking cultures that left them vulnerable to abuse. "The idea that a product could make your life worse was not in anyone's perception," said Mr Hochmuth, who left Instagram in 2014.

That perspective helps explain the shock many founders felt when the Internet grew into the foundation of global culture and commerce, and products they had built as quirky experiments became pieces of critical infrastructure.

"No one was thinking about 'Wow, in 15 years, billions of people are going to be using this site every day,'" said Andrew McCollum, 34, one of Facebook's founders, who left the company in 2006 and is now chief executive of Philo, an Internet TV company. "The goal was 'How do we create something great?' - not 'What's our plan for world domination?'"

Twitter, another company started by young idealists, is the latest tech giant to put itself under the microscope. In a series of tweets early this month, Jack Dorsey, Twitter's chief executive, said the company was trying to improve the health and civility of its platform after years of neglect. "We didn't fully predict or understand the real-world negative consequences," Mr Dorsey, 41, wrote. "We acknowledge that now, and are determined to find holistic and fair solutions."

You could chalk these statements up to self-interest. But Maureen Taylor, a leadership communication expert who frequently coaches tech executives, said this kind of earnest self-examination was becoming more frequent among founders. "As you get older, you realise your responsibilities are bigger," she said. "People are becoming very thoughtful about the ramifications of technology, and remembering that the whole point was to make the world a better place."

The tech industry's stereotypical accessory used to be the hoodie. Today, it might as well be the Baby Bjorn. There are a lot of new parents among tech elites, including Mr Zuckerberg and Kevin Systrom, 34, a co-founder of Instagram. And parenthood seems to be shaping their attitudes. In an interview with The New York Times this year, Mr Zuckerberg cited his children as one of the reasons he was so focused on fixing Facebook.

"It's important to me that when Max and August grow up that they feel like what their father built was good for the world," Mr Zuckerberg said.

Chamath Palihapitiya, 41, an early Facebook executive who now leads the venture capital firm Social Capital, said: "Before fatherhood, I believed that enabling my children to grow and explore through technology would be an obvious edge and something I'd support. Increasingly, what I see is a detached generation of kids living behind screens."

Silicon Valley works a bit like a forest - as old trees decay and die, they decompose and fertilise the next generation of growth. And today's largest tech companies are beginning to show their age. Facebook is 14 years old, Twitter is 12 and Google, at 20, is now nearly as old as Microsoft was in 1998, when Google was started.

The tech industry's maturity may be a sign of cyclical renewal.

If history is any indication, that cycle will repeat itself and a new crop of young tech leaders will emerge. But hopefully they'll learn from the mistakes made by their predecessors. Technology is too important now, and we can't afford another generation of naïveté. NYTIMES