Yahoo is anything but. It's turning 20 next year ... that's like 1,000 years old in internet time. Think of Tumblr as a much-needed injection of youth serum -- Mayer figures she can breathe new life into Yahoo’s beleaguered brand by buying a big pile of those much-coveted 18-to–24-year-olds. If it costs a billion dollars, so what? Yahoo’s biggest challenge will be how to wring money out of all those fresh young eyeballs. And they're starting off on the right foot because they're keeping Tumblr's branding as is. After all, those fresh young eyeballs probably won't take too kindly to Yahoo coming in and totally rocking their Tumblr world right off the bat. But if Tumblr hasn’t been able to make money, why should we think Yahoo can crack the monetization code? Tumblr’s board came to the conclusion that Tumblr had gone as far as it could with its current leadership, so it arranged a marriage where both sides bring something the other needs. Tumblr is run by smart kids who built an audience, but don’t know how to make money. Yahoo is run by adults (though those mired in the Yahoo-work-from-home debate might argue otherwise) who built a machine that converts pageviews into dollars. So maybe it all works out. Maybe in the short term Tumblr loses some cool kids who don’t want to be associated with Yahoo, but in the long term continues to grow. Maybe Tumblr becomes the third-biggest social platform after Facebook and Twitter -- one that’s younger and hipper. Maybe Yahoo finds a way to squeeze billions out of all those Tumblrers without ruining the experience and driving the audience away. Get the full story at HubSpot and John Batell's Seach Blog