Hello, Nothing can be conclusively said before a thorough evaluation for your brother. However such forgetfulness may be related to medical factors like thyroid, anemia, other endocrinal irregularities, etc, psychological factors like inattention, stress, depression, intellectual impairment, learning disability, etc, environment factors like bullying, neglect, etc. Hence please seek a consultation with a psychiatrist near you for comprehensive assessment. Some physical and psychological tests may be required to assess in detail. Hope this helps you. Best wishes for your health and future..