Patrick Schwarzenegger, the 17-year-old super-spawn of Arnold and Maria, limps—but never once winces—through the upper courtyard of the Brentwood Country Mart. During the previous night's soccer match, Patrick, a Brentwood High defender, caught a charley horse, and his leg is still stiff. He's wearing slim black pants, a form-fitting red-and-navy-plaid shirt, and—he's proud of these—the black Palladium fold-down military boots that he bought on a business trip to the Magic clothing convention in Las Vegas. He is six feet one but seems taller—and not just because he's sporting a side-swept, gravity-defying updo. A princely local celebrity accrues to Patrick, and the limp does nothing to diminish it.

Even if you've never been inside the Brentwood Country Mart, you've likely seen its farmhouse-kitschy façade. Since the dawning of the "Stars—They're Just Like Us!" era, this upscale shopping center has become the Most Photographed Barn in America. It's where—EXCLUSIVE!—Jessica Alba and her toddler, Honor, were spotted at the Pulp & Hide Candy Alley; where Jennifer Garner and elder daughter Violet met up with hubby Ben Affleck and baby Seraphina for quality family time; and where, last October, accompanied by his do-it-all mom, Maria Shriver, Patrick was snapped leaving Maha yoga studio with no shirt on.

The paparazzi had caught Patrick there a couple of times before, but never like this. TERMINATOR IN TRAINING ran the headline in the U.K.'s Daily Mail, which juxtaposed a pic of lean and sinewy Patrick with one of his jacked-up father. A blogger for Best Week Ever wrote, "Why do some people have it as easy as a haircut and a couple of workouts to become HOT AS SH*T." But Patrick, who knows a little something about the celebrity machine, isn't trying to capitalize on tabloid fame.

"I'm in a fork-split path right now," he says. "My mom raised me with the idea of doing public service, and I definitely want to go in that direction. But I also want to follow in my dad's entrepreneurial footsteps."

When your chromosomes are part Kennedy, part Schwarzenegger, few advantages elude you. But in the eyes of both sides of the family, they aren't worth anything unless you do something with them. At 17, Patrick has expectations to live up to. "The Kennedy-Shrivers were much more hands-on—they were brought up with the idea that doing good was fun," says Laurence Leamer, a Kennedy family biographer who has also written Fantastic: The Life of Arnold Schwarzenegger. "And there's no more competitive person in the world than Arnold Schwarzenegger." This can weigh on a kid.

"You do things at a young age in this family," says Patrick's 21-year-old sister Katherine, the author of Rock What You've Got: Secrets to Loving Your Inner and Outer Beauty From Someone Who's Been There and Back. As of yet, neither Patrick's sister Christina, who's 19, nor his 13-year-old brother, Christopher, has sought the spotlight. "Patrick and I have bonded," Katherine says, "over the fact that I wrote a book young and he's already started a business."

That business is called Project360, the philanthropically oriented, increasingly profitable (mid-five figures, net, in 2010) clothing line Patrick cofounded two years ago, at 15. The company donates 10 percent of all its sales to a variety of causes—and that percentage isn't arbitrary. "My grandmother always said," Patrick recalls, "when you receive a paycheck, you always have to put a certain amount to your savings, and 10 percent right away to charity."

Patrick is trying to raise the profile, and the charitable output, of Project360, whose T-shirts, bracelets, and hoodies have been carried in Bloomingdale's and Henri Bendel, worn by the likes of Reggie Bush and Eva Longoria, and featured on Access Hollywood. At a café in the Country Mart, he and his partners, Nick Sheinberg (his oldest friend) and Kimberly Barth, met to discuss the pros and cons of using English-language appliqués like UNFORGETTABLE (benefitting Alzheimer's research) and SURVIVOR (cancer-stricken children) as the company expands into Asian markets. They also selected fabrics for their first men's line, due this winter, consisting of luxe sweats, windbreakers, and, in a nod to Patrick's father, leather bomber jackets.

In one recent for-profit venture, he proved adept at getting out of trouble—a skill that is every bit as valued by the Kennedys as by the Schwarzeneggers. It was last Halloween, when Patrick cohosted "the biggest party any high-school kid has ever been to," in Pacific Palisades. "There were, like, 600 people there," he says. "We flew in a rap group from the East Bay called the Pack." The cops busted the party, handing out multiple citations for underage drinking. Coming just a few weeks after the shirtless-yoga pic, it led to Patrick's first brush with less-adoring coverage. "They're glad I had fun with it," Patrick says of his parents, "but they weren't happy with how it was portrayed in the media."

"It looks like dis apple doesn't fall too far from de tree," wrote an LA Weekly blogger, citing as evidence the Governator's "hard-partying ways during his Venice body-building days." But the blogger was only half right. He didn't mention the entrepreneurial zeal behind the venture (admission was $20). Referring to his investment in the event, Patrick says proudly, "I easily made it all back."

Nor is the young Schwarzenegger opposed to selling his image—he just signed on with L.A. Models, which has plans to push him for the Ralph Lauren and Armani campaigns. He's doing it to "inject some capital" into Project360 and to "get comfortable in front of the camera." But modeling "isn't going to be my permanent job. There's a lot of other things I want to do."