So why would Yahoo – the original king of Internet discussion groups – pay over $1 billion for a simple little blog-publishing tool like Tumblr? Doesn’t the giant Web company have the ability to create its own application that lets people post words and pictures online? Of course it does.

No, Yahoo isn’t buying a technology company so much as the community that uses it. It paid a billion bucks for Tumblr for the very same reason that Facebook paid a billion dollars last year for web-sharing app Instagram: for the kids.

That’s right, the net’s biggest corporations are willing to pay through the nose to acquire teenagers – that coveted yet slippery demographic for whom the Web is a tired old workplace, Facebook is their parents’ (or grandparents’) social network, and Yahoo has something to do with stock quotes and sports scores. A new generation of apps and networks – from Tumblr and Instagram to Snapchat and Pinterest – has emerged alongside this new generation of users, and if traditional companies can’t beat them, they may as well buy them.

Teens and young 20-somethings have been drifting away from what over-30s people think of as the Internet for years now. The World Wide Web is flat, static, and largely dependent on desktop and laptop computers to work right. Younger people are much less likely to connect to the net – or to each other – through these cumbersome devices than they are to use smartphones.

The mobile Web, as it’s called, works differently. It’s navigated by thumb, through separate apps, and in shorthand. The big websites and search engines of yesteryear (well, at least yesterweek) – like Yahoo, for example – just weren’t built for this kind of light engagement. They’re meant for keyboards and mice, not swiping and txt shorthand.

Meanwhile, the corporations running big websites and social networks might seem like upstarts to older users, but to young people they are pre-existing conditions of the universe. Just as the Beatles might as well be Frank Sinatra, Facebook might as well be Microsoft or IBM. The big established networks just aren’t cool. Mark Zuckerberg is already almost 30. Plus, his social network – just like those of his peers at Google+ – feels unnecessarily complex and requires a big commitment.

Everything one does in the adult social media world goes down on one’s permanent record. The experience on a site like Facebook is so involved – friends lists, updates, photo streams, timelines, advertisements – from the teen perspective, it’s a Whole Big Thing. Compare that to something like Instagram. You take a picture and it goes up and out. That’s it. Or Snapchat: You take a picture and it goes to a friend, and then it disappears. How cool is that?

The less weighty and permanent and stickily complex a social networking experience, the less it feels like it’s the province of marketers, too. Every keystroke, recommendation, follow, like and update is recorded and stored. Kids are becoming aware that the more involved the data footprint they create somewhere, the more it will be used against them by big data researchers looking to predict their future activities and then market to them the things they don’t yet know they’re about to desire. Which is just creepy.

This is why the real job of younger companies is to prove they are not your parents’ social apps. That’s why it becomes particularly challenging when a hip “young person’s” social app is swallowed by a big, old, uncool Web company.

After Tumblr’s base of young users found out about the sale, they went into a near state of panic. Many posted on Twitter and elsewhere how this represents the end of an era, and how they are now destined to move on to the next frontier.

For its part, Tumblr is working hard to prove it still has indie cool street cred. In his blog post responding to the angst around his “selling out,” Tumblr founder David Karp sounded like a young Steve Jobs by insisting “how awesome this is.” Then, as if to prove Tumblr is still cool enough to do naughty things even though it’s now owned by a zillion-dollar corporate conglomerate, he signed his post, “F*** yeah.”

Maybe that’ll work, but it looks to me like Tumblr has gone from being cool to trying to sound cool. And we all know where that leads.