 Adults with ADHD are diagnosed under the same criteria , including that their signs must have been present by the age of six to twelve . Questioning parents or guardians as to how the person behaved and developed as a child may form part of the assessment ; a family history of ADHD also adds weight to a diagnosis . While the core symptoms of ADHD are similar in children and adults they often present differently in adults than in children , for example excessive physical activity seen in children may present as feelings of restlessness and constant mental activity in adults . 
