Yahoo! is under two decades old and is already showing signs of age. Tumblr, the cool blogging platform, represents a new generation.

This split marks both a challenge and an opportunity for the firms, after the announcement that Yahoo! is buying the six-year-old startup for $1.1 billion, mainly in cash.

"Yahoo users are behind the curve, Tumblr users too cool for school," said Arvind Narayanan, a Princeton University computer scientist, in a tweet.

"From this POV (point of view) the acquisition seems ironically appropriate."

Tumblr could be key to Yahoo! because of its popularity with younger Internet users. A survey this year conducted by the online data group Survata found Tumblr more popular than Facebook among those aged 13 to 25.

"Yahoo skews toward older demographics. Tumblr is ridiculously strong among Millennials," said a tweet from Brian Solis, analyst with Altimeter Group.

Some comments posted on Tumblr as the news broke highlighted this generation gap, as if their parents were intervening to spoil the party.

"YAHOO, CLOSE TUMBLR AND YOU'LL DIE!" one Tumblr user wrote.

Another wrote: "Dear Yahoo ... If you change anything, we will show up at your headquarters with fire and pitchforks. Don't try us."

Still another posted: "Please leave Tumblr alone. You acquired it for the cool factor... Don't tinker with it; don't change it ... Leave it alone."

Yahoo! chief executive Marissa Mayer, in announcing the deal, pledged to allow Tumblr to remain independent, while integrating technology and advertising opportunities.

"Per the agreement and our promise not to screw it up, Tumblr will be independently operated as a separate business," Mayer said in a statement.

"David Karp will remain CEO. The product, service and brand will continue to be defined and developed separately with the same Tumblr irreverence, wit, and commitment to empower creators."

Karp echoed those comments, saying in his own blog post: "We're not turning purple," in reference to the Yahoo! portal's signature color.

But some analysts it could be hard for Mayer to keep her promise of keeping Tumblr independent while seeking ways to make the deal pay off.

"If I'm the CEO of Tumblr I would be concerned," said Daniel Odio, senior vice president of California-based Internet firm Share This, who has been involved in a number of technology startups.

"Marissa is promising to keep it independent, but I just don't buy it. Just looking at history, I would say that the culture that makes Tumblr special is going to change," Odio told AFP.

Roger Kay, analyst with Endpoint Technologies Associates, also was skeptical about integrating the two different firms.

"There's a particular thing in the hacker culture, and it is difficult for a large bureaucratic company like Yahoo! to keep that alive," Kay said,

"Yahoo! once upon a time was an entrepreneurial company with all the spirit that Tumblr has, but they have been though a number of retreads. The best programmers have long since gone to other places."

Kay said the deal also could prompt some of the staff at Tumblr, many of whom will get a big windfall from the deal, to cash out and move elsewhere.

"Marissa Mayer might have thought that she was buying a staff, but this is a place where you can least expect people to stick around," Kay said.

"What they are buying is a bunch of code, and the customers and maybe the revenue stream," he said.

"You can't assume you're buying the talent. The talent likes to decide which master they want to serve."