Rightly or wrongly, many people have a picture in their minds of the average online gamer, and it probably involves someone not yet old enough to vote, huddled in their parents’ basement killing dwarves with mystic powers in games like World of Warcraft. A growing category of what are called “social games,” however, appeals to a much different demographic, according to a recent study. The study — sponsored by PopCap, creator of popular social games such as Bejeweled and Insaniquarium — looked at game players in both the United States and the United Kingdom, and found that the average player of these online social games is a 43-year-old woman.

More than 24 percent of those who responded to the survey (full results in PDF form here) said they regularly play social games, a category that includes Facebook games such as Farmville, Mafia Wars and Happy Aquarium. According to survey company Info Solutions Group, that level of response suggests a total social gaming population of approximately 100 million. Social gamers were defined as those who said they play games on social networking sites such as Facebook and MySpace at least once a week. The market for social games has been growing so quickly that companies that make them, such as Zynga and Crowdstar, have become investment and acquisition targets.

Social gaming seems to appeal to a much older demographic than traditional video games, perhaps in part because social games are easier to play for short periods of time, are largely free, and don’t involve sophisticated equipment or gratuitous violence. According to a recent survey by Royal Pingdom, the average age of social networking site users in general is also older — the largest single group is between 35 and 44 years of age. More than 60 percent of Facebook users are over 35.

The PopCap study showed that 55 percent of all social gamers in the U.S. are women, as are almost 60 percent of those in the UK. The average age in the U.S. is 48, which is substantially older than the 38-year-old average in the UK, and 46 percent of American social gamers are 50 or older, compared with just 23 percent in the UK. Only 6 percent of all social gamers are age 21 or younger.