LOS ANGELES — As the Twitter juggernaut roars across the Internet seemingly unobstructed, meet at least one guy who has angrily placed himself in its path.

Bob Baker disdains Twitter, considers it one of the 21st century's great wastes of time and (brace yourself Tweeters), has no interest in knowing when you get up in the morning, when you go to bed at night or what you do during the hours in between.

"What you're probably hearing are the frustrations of an old man," the 60-year-old Los Angeles writer says as he wraps up a brief anti-Twitter rant (one he might have come close to fitting into a 140-character Tweet if he'd just break down and embrace the thing).

Baker is a Facebook man and, like the proverbial old dog, figures he may not be capable of adapting to yet another new social network.

While it's still too early to say clearly whether things like personality or age drive people to one social network over another, clinical psychologist Karen North says some patterns are emerging.

"Twitter immediately grabbed the young texting set, people who like to send out little blasts of information," she says.

Meanwhile, Facebookers are seen as older, less into expressing their most random thoughts and more into leisurely online socializing.

And MySpacers? Some compare their site of choice to last year's hot night spot that has lost much of its buzz to younger joints like Twitter.

Twenty-year-old actress Chelsea Staub still keeps Facebook and MySpace pages but has mostly defected to Twitter, saying she has been on the site nonstop for the past couple of months.

"I'm pretty addicted," she giggles, adding she realized just how addicted when she boarded a Los Angeles-bound flight in Chicago and felt her heart leap when she discovered the plane had WiFi. That meant she could Tweet all the way home.

"At first I'm like, All right!" recalls Staub, who stars opposite the Jonas Brothers in their new TV series. "Then I'm like, This may be a problem. I don't write my mom or do anything else anymore."

Twitterites tend to skew toward Staub's generation, North says, because they grew up using cell phones as extensions of their bodies.

Some have even been known to use them to text-message people standing right next to them, often to pass on such vital information as their immediate need to use a bathroom. They were made for Twitter.

By comparison, Facebookers prefer more extended wireless socializing to getting and sending snippets of chatter.

Facebook's own data says its fastest-growing segment of users is over 35. One is Paula Symons, a 58-year-old corporate communications executive from Madison, Wis., who signed on 18 months ago and quickly became Facebook pals with the friends of her 26-year-old son.

"Which is very weird," she says. "But now I'm finding all these people I know who are my age."

In the old days, such people might have been the ones who gathered at the neighborhood bar after work or at a weekend picnic to play games and talk.

These days, however, after posting photos and exchanging quips, many get caught up in one of the many Facebook-linked games, perhaps the one in which players pretend to be farmers and spend hours milking cyber cows and chasing cyber chickens.

"I don't have enough time to do this myself," North quickly says of that game. "But I know people who are obsessed with it."

And remember MySpace? It started out attracting the young and hip with its graphics and music platform.

But Jeffrey Cole, who runs the Center for the Digital Future at USC's Annenberg School for Communications, now compares it to last year's hot night spot.

It still draws its share of people. Just not the really coolest ones anymore.

"One thing we have seen for a while is that for teenagers, social networking sites are like nightclubs," Cole says. "When a nightclub becomes too popular, or the uncool kids start showing up, the cool kids are out of there."

Don't tell that to Isabella Galeazzi, a student at a Southern California middle school who says all the coolest kids in her classes can still be found on MySpace. Old people, she says, inhabit Facebook and celebrities have taken over Twitter.

Galeazzi estimates she spends three or four hours a day on MySpace.

"Friends get mad because I can never hang out with them at the mall," she says.