Yes, boys are often inattentive and hyperactive. Girls do have the disorder but are usually not hyperactive or a conduct problem. Girls are mistakenly called lazy, slow or spacey. Women and girls are often misdiagnosed as anxious or depressed. ADHD children do well.
Worst advice is to try harder as symptoms increase.
Brain imaging shows areas are inhibited by increased effort. Brain imaging demonstrates abnormal anatomy and physiology in ADHD as in other disorders, such as the medical abnormalities in diabetes or asthma. It is underdiagnosed especially in girls. No, it is physically based. It is a genetic or developmental disorder.