A grinding sound, somewhere between a rattle and a rumble, erupted over the suburban New Jersey hill. The figures, clad in motorcycle leathers and helmets, started to appear, one, two, three, until there were almost 20, crouched on skateboards, like a squadron of roller-villains.

One by one, the skaters rounded a turn, dropping a gloved hand to the asphalt as they scraped their wheels in a slide, taking care that nobody crossed into oncoming traffic and found themselves splattered across the grill of a Buick.

At the bottom of the hill, the leader of the Bergen County Bombers, as this gang of skateboarders is known, wrestled the black motorcycle helmet from his head, revealing a mortgage broker with gray flecks in his beard and the crow’s feet that come from decades in the white-collar trenches.

“It’s a total midlife crisis,” said the group’s leader, Tom Barnhart, 47, of Cresskill, N.J., who started skateboarding two years ago for the first time since the Carter administration. His life, he said, had been in a rut. “My kids grew old, so I got a dog. My dog grew old, so I got a skateboard.”

“That was what knocked the cobwebs out of my head,” he added.

Forget the little red sports car: The new symbol for midlife crisis is the skateboard. Graying members of Generation X, and even their older brothers, are reclaiming their youth and rebellious streak by hopping back on a skate deck. Some are even showing off old tricks in the skate park.

“The skate geezers are having their revenge,” said Michael Brooke, the publisher of Concrete Wave, a skateboard lifestyle magazine based in Ontario, Canada.

Indeed, the skate geezer is becoming something of a trope in popular culture. A recent satire in The Onion was headlined, “43-Year-Old With Skateboard Not Fooling Anyone,” complete with a close-up of Tony Hawk, the skateboarding superstar, looking a bit weathered in his helmet. Dave Carnie, the gonzo writer and former Johnny Knoxville sidekick on “Jackass,” introduced a line of decks with Tum Yeto skateboards called Fat Old Guy Skateboards to appeal to skaters who “just awoke from a coma and still think it’s 1984,” he said.

And why not? Skateboarding itself is entering middle age. Like the older members of Generation X, the sport was born in the ’60s. The pioneers are now at an age when they’re paying off mortgages and their children’s college tuition.

“Tony Alva and I have joked about it,” said Stacy Peralta, who, along with Alva, was a member of the legendary Z-Boys skate team in Venice, Calif., in the 1970s. As detailed in Peralta’s 2001 documentary “Dogtown and Z-Boys,” they would sneak into unoccupied suburban homes and drain swimming pools to skate in them.

“When we were kids, it was so new, we could never imagine doing this when we were 50,” he said. “The idea that my dad could be doing the same thing I was doing in a swimming pool was unheard of.”

But now Peralta is 52, the father of a 21-year-old son, and he is doing precisely that, spending his weekends at a state-of-the-art skate park near his Santa Monica, Calif., home.

“It’s got beautiful transitions and voluptuous shapes, unlike the dangerous pools we rode as kids,” Peralta said. “They finally figured out how to design a skateboard park that is forgiving to middle-aged men.”

Longboards

It’s not only the parks that have become more forgiving. The skateboards themselves are now smoother and grown-up-friendly, thanks to a booming segment called longboards.

Longboards are the luxury sedans of the skateboarding world. They are usually about 40 to 48 inches long, compared with traditional street decks, which are around 32 inches. Fitted with bigger, softer wheels to roll over sidewalk cracks and pebbles, they are built for cruising and carving, not tricks and aerials, and appeal to riders who no longer risk broken bones by grinding rails and ollying curbs, as they did as teenagers.

“It’s like snowboarding,” said Brian Petrie, the founder of Earthwing, a skateboard company based in New York. “Anyone can learn to push, turn and stop in no time.”

Leading longboard manufacturers like Honey Skateboards of Colorado, Bustin Boards of New York and Original Skateboards of New Jersey report a surge in sales among older riders. That corresponds to a noticeable graying of the skateboard demographic. The number of skateboarders over 35 has nearly doubled in the past decade, to 742,000, from 404,000, and now accounts for 10 percent of the market, according to the National Sporting Goods Association, a trade group in Mount Prospect, Ill.

Even though longboards are more forgiving to older riders, the feeling they inspire is one of eternal youth, devotees said. A skateboard has a countercultural appeal that a single-speed bike or a tennis racket does not. It is a talisman of youthful rebellion, a rude gesture to Ward Cleaver responsibility.

Bad-boy image

Many middle-aged skaters grew up reading about the outlaw exploits of skaters like the Z-Boys. And while they may not have sneaked into backyard swimming pools themselves, the sport’s subversive bad-boy ethos became as ingrained as the scars on a veteran skater’s elbows. As every high schooler knows, skaters have always been the teenage thrill-junkies who tended toward punk rock, tattoos and C-minuses.

Decades later, that renegade spirit lingers for middle-aged cubicle captives who return to the fold. Their comeback ride is like the scene in “Easy Rider” where Billy and Captain America remove their watches and toss them roadside.

“When you step on a board, all of your muscles are firing at the same time to do one thing,” said Chadd Hall, a 39-year-old information technology manager in Atlanta who slips out of work at lunch to ride his 39-inch Rayne skateboard. “You don’t have a whole lot of time to think about all the things that make up a 40-year-old’s life: how the kids are doing in school, all the different people at work coming at you needing something. All of that fades away.”

The anti-authority mystique is not lost on Joe Borress, 41, a contractor from Greenwich, Conn., who took up skateboarding two years ago and now commutes from Grand Central Terminal to his office in SoHo on a 38-inch Bustin Maestro. “Skateboarding has that association: youth, punk, rebel,” he said. “It has that connotation of being bad.”

It’s not just men. Annie Messick, a 36-year-old housewife in Gulf Breeze, Fla., who took up longboarding last year, put it this way: “It is my mellow that I have been seeking for all my life.”

That mellow, it should be noted, is not without a price. Don Bailey, a news technology manager for a television station in Atlanta, occasionally shows up at work with a limp. Colleagues don’t bother asking anymore.

“I found out the asphalt is much harder,” said Bailey, who is at the older end of the skate-geezer spectrum at 53. “You’re skinned up, with skinned elbows, so you stop at CVS on the way home and buy bandages, cover up as best as you can before wife sees it.”

For those who ride in packs, skateboarding is not just a rebellion against age but also against middle-age isolation. The sport affords skaters in their 40s and older a chance to hang out with buddies in a way they have not since they married and had children.

More than once, Gary Saenz, a 52-year-old quality-assurance specialist in Germantown, Md., has been skating in an industrial park or new housing development when a police cruiser has rolled up ominously. Bracing for a tense standoff with The Man, he usually just gets a quizzical look.

“They realize I’m not a teenager,” he said, “just an overweight dude with gray hair.”