For many of us who grew up in the 1990s and 2000s, attention deficit hyperactivity disorder — better known as ADHD — seemed like a condition for kids. But that perception is changing: Of the more than 15 million adults in America diagnosed with ADHD, about half of them got that diagnosis in adulthood. Laura Knouse, a licensed clinical psychologist and professor at University of Richmond, says that the condition can be a challenge to diagnose, leading to delays.