Since 1930, the Boy Scouts of America has helped younger boys through Cub Scouting. It is a year-round family program designed for boys who are in the first grade through fifth grade (or 7, 8, 9, and 10 years of age). Parents, leaders, and organizations work together to achieve the purposes of Cub Scouting. Currently, Cub Scouting is the largest of the BSA's three traditional membership divisions. (The others are Boy Scouting and Venturing.)
http://www.scouting.org/Media/FactSheets/02-502.aspx

Boy Scouting is a year-round program for boys age 11 – 17. Boys who are 10 may join if they have received the Arrow of Light Award or have finished the fifth grade. Boy Scouting is a program of fun outdoor activities, peer group leadership opportunities, and a personal exploration of career, hobby and special interests, all designed to achieve the BSA's objectives of strengthening character, personal fitness and good citizenship.
http://www.scouting.org/Media/FactSheets/02-503.aspx

Venturing is a youth development program of the Boy Scouts of America for young men and women who are 14 (and have completed the eighth grade) through 20 years of age. Local community organizations establish a Venturing crew by matching their people and program resources to the interests of young people in the community. The result is a program of exciting and meaningful activities that helps youth pursue their special interests, grow, develop leadership skills, and become good citizens.
http://www.scouting.org/Media/FactSheets/02-388.aspx

Sea Scouting is a coed outdoor program for young adults 14 – 20 years old and their adult advisors. Discover the resources that make Sea Scouting the place to be.
http://www.seascout.org/

Exploring is a worksite-based program. It is part of Learning for Life's career education program for young men and women who are 14 (and have completed the eighth grade) through 20 years old. Exploring's purpose is to provide experiences that help young people mature and to prepare them to become responsible and caring adults. Explorers are ready to investigate the meaning of interdependence in their personal relationships and communities.
http://www.learningforlife.org/exploring/

Varsity Scouting is a program for young men who are at least 14 years of age but not yet 18. It provides options for young men who are looking for rugged high adventure or challenging sporting activities and still want to be a part of a Scouting program that offers the advancement opportunities and values of the Boy Scouts of America.
http://www.scouting.org/Media/factsheets/02-923.aspx