What age does ADHD occur?

ADHD can be diagnosed at any age, but it is usually first diagnosed in childhood or adolescence. Symptoms of ADHD may start as early as preschool or kindergarten and may continue into adulthood. ADHD is thought to be a neurodevelopmental disorder, which means that it is thought to be caused by abnormal brain development. The exact cause of ADHD is not known, but there are likely multiple factors involved, including genetics, environmental factors, and prenatal factors.