| Country | Military service age and obligation |
| Bahrain | 17 years of age for voluntary military service; 15 years of age for NCOs, technicians, and cadets; no conscription (2008) |
| Bangladesh | 16 years of age for voluntary military service; 17 years of age for officers (both with parental consent); conscription legally possible in emergency, but has never been implemented (2008) |
| Barbados | 18 years of age for voluntary military service (younger requires parental consent); no conscription (2008) |
| Belarus | 18-27 years of age for compulsory military service; conscript service obligation - 18 months (2005) |
| Belgium | 18 years of age for voluntary military service; conscription suspended (2008) |
| Belize | 18 years of age for voluntary military service; laws allow for conscription only if volunteers are insufficient; conscription has never been implemented; volunteers typically outnumber available positions by 3:1 (2008) |
| Benin | 21 years of age for compulsory and voluntary military service; in practice, volunteers may be taken at the age of 18; both sexes are eligible for military service; conscript tour of duty - 18 months (2006) |
| Bermuda | 18-23 years of age; eligible men required to register for conscription as needed into the Bermuda Regiment, which is largely voluntary; term of service 39 months (2007) |
| Bhutan | 18 years of age for voluntary military service; no conscription (2008) |
| Bolivia |  18-49 years of age for 12-month compulsory military service; when annual number of volunteers falls short of goal, compulsory recruitment is effected, including conscription of boys as young as 14; 15-19 years of age for voluntary premilitary service, provides exemption from further military service (2009) |
| Bosnia and Herzegovina |  18 years of age for voluntary military service; conscription abolished January 2006; 4-month service obligation (2009) |
| Botswana | 18 is the apparent age of voluntary military service; the official qualifications for determining minimum age are unknown (2001) |
| Bouvet Island | void |
| Brazil | 21-45 years of age for compulsory military service; conscript service obligation - 9 to 12 months; 17-45 years of age for voluntary service; an increasing percentage of the ranks are "long-service" volunteer professionals; women were allowed to serve in the armed forces beginning in early 1980s when the Brazilian Army became the first army in South America to accept women into career ranks; women serve in Navy and Air Force only in Women's Reserve Corps (2001) |
| British Indian Ocean Territory | void |