Geoffrey Brow, an attorney for Dell Computers in Austin, Texas, doesn’t get out much anymore. The last concert he attended was a reunion show by seventies rockers Grand Funk Railroad. He left early. “It was too loud and people were jostling into me,” he says. To the extent that he listens to music at home, he prefers classic rock like the Rolling Stones. “I’m not completely immune to new stuff,” he says. “I do like Coldplay.” At the gym, Brow rides a stationary bike and wears a heart monitor. After work he enjoys single-malt Scotch and sometimes watches baseball (“but only non-expansion teams”). He’s usually in bed by 10 P.M.

Brow is 36 years old.

Now, feeling old is nothing new. Somewhere in the neighborhood of 30, every guy gets a few physical reminders that he’s not a kid anymore. The back begins to creak, fatigue comes more quickly, and hair starts disappearing from some places (and showing up in others). But acting old, wholeheartedly adopting the lifestyle and mannerisms of a man a generation or more older, is something different. It’s a choice, and for a man who has 50 or 60 years of life left, it’s a pathology. Rather than downplay middle age with a Sufjan Stevens T-shirt and the newest iPhone, these guys sprint from their youths, behaving like Uncle Charley from My Three Sons while still squarely in the prime of life. They succumb to Grandpa Syndrome.

“It’s a weird twist on the phobia of being the oldest guy in the club,” says Christian Lander, author of Stuff White People Like. “Remember seeing that 45-year-old dude in 1999 off in a corner kinda dancing to himself? You want to make sure that’s not you, so your preemptive move is not going out at all once you hit 35—or even 30.”

Beyond the specter of the old man in the club, the sheer anxiety of keeping up with pop culture can trigger premature aging. Who with full-time employment has time to track every hookup on The Hills, every new Facebook application, every new Lil Wayne release? Especially when there’s a sale on at Waldenbooks or it’s Shark Week on Discovery Channel.

At 43, Brad Anderson, a Manhattan screenwriter and director, is “done” with answering his cell phone, one he describes as “some old thing without the BlackBerry stuff on it.”

“The more I disengage myself from what’s going on around me,” Anderson says, “the less miserable I’ll be. Besides, television, music—it’s all become crap.”

This is the stock declaration for a man with advanced Grandpa Syndrome. As far as he’s concerned, there hasn’t been anything worth being awake for past midnight since Tom Snyder went off the air.

“You hear people whining that there’s nothing authentic anymore,” says David Browne, 48, author of Goodbye 20th Century: A Biography of Sonic Youth. “Paris Hilton, Feist, the horrible singers on American Idol...” He continues in a mock grandpa voice: “‘Oh, but in the nineties, man! Music was real. The economy was rolling. We had Puck on The Real World!’”