Community-Based Gang Intervention Act This bill amends the Juvenile Justice and Delinquency Prevention Act of 1974 to authorize grants to nonprofit community-based organizations for community-based gang intervention. It adds a definition for the term "community-based gang intervention." Additionally, the bill modifies the qualifications of State Advisory Group members to include representatives of community-based gang intervention agencies and to specify that a representative of a nonprofit organization includes a person with a special focus on community-based gang intervention. Finally, the bill adds, as a purpose area under the Incentive Grants for Local Delinquency Prevention Programs, providing community-based gang intervention and gang prevention activities to juveniles and their families.