That's a dramatic increase from the last such study in the 1960s when 22 percent of Americans reported being arrested by the same age.
The research relied on surveys of over 7,000 young people taken over the last 11 years. The arrests were for a variety of offenses, including truancy, underage drinking, shoplifting, robbery, assault, and murder. Only minor traffic offenses were excluded.
Some experts say the new numbers come as little surprise, given several decades of tough on crime policies.