The group says 42 percent of its new members in 2009-10 were ages 29 to 49 and during the past 10 years the number of members under 30 has grown by 63 percent, USA Today reported Monday.
American Mensa National Chairwoman Elissa Rudolph told the newspaper the group is aiming to get "more people involved and younger people more involved."
Part of the effort is Saturday's National Mensa Testing Day, in which hopefuls will take the group's own admissions test or one of 200 other tests, such as the Stanford-Binet, the Miller Analogies Test, the GMAT or the GRE.
To qualify, applicants must score in the top 2 percent of the test-takers. The fee for American Mensa's test is $40, the group says on its Web site.
Mensa member Alexis Wise, 19, a sophomore at Yale University, told USA Today the benefits of being a Mensan include learning from brilliant people in non-academic settings.
"I have the coolest group of friends, and that's only grown over the years," she said. "I've learned so much."