A new report this week suggests the Illinois legal system should get acquainted with a new demographic: “emerging adults.”Researchers from Columbia University in New York today released a snapshot of 18- to 24-year-olds in the justice system, titled “Emerging Adult Justice in Illinois: Towards an Age-Appropriate Approach.”Citing numbers from 2013, they show people between ages 18 and 24 made up about 10 percent of the state’s population, but accounted for 34 percent of its arrests and 28 …