MINNEAPOLIS—Jef VanSyoc doesn't come across as the head of an exclusive social club. He has thick dreadlocks and a piercing under his lip. He asks to be called "The Dark Lord" instead of president or executive director. That's because he isn't running a golf course or a cigar lounge but the "Dark Arts Blood Bowl," a members-only skateboard park where skaters can age in peace.

"The skateparks are a little crowded, and sometimes the kids are snot-nosed punks," says the 38-year-old Mr. VanSyoc, whose 12 members pay a $500 initiation fee in addition to $80 a month in dues. "It's guys getting away from their wives and kids."

Despite a decadelong boom in free public skateboard parks, some older skaters are turning to private cooperatives, or "key clubs," that are open to a handful of members and guests. They charge dues and maintenance fees that allow members—most of whom are over 30—to ride in a controlled environment free of the nonpaying skaters, scooters and Rollerbladers who clog up public skateparks.

There's no official listing of skateboard key clubs, since being hidden is sort of the point. Most are tucked away inside industrial warehouses, and their members tend to be cagey about the location and stingy with the invitations. In addition to Minneapolis, cities including Omaha, Neb., Portland, Ore., Madison, Wis., and Seattle, all have some kind of private skate club scene. There are probably dozens more: In the Chicago area, temporary clubs pop up every winter. Other parks, like New York's now-defunct Autumn Bowl, have come and gone.

The growth in key clubs has risen in tandem with skaters' age. The first skateboarders are now well into their 50s, leaving an abundance of over-30 skaters with the means and attitude to maintain a private facility. Also, while younger skaters tend to prefer the street style of skateboarding that plays out in downtowns and schoolyards, older guys are drawn to ramps and bowls that are easier on the knees.