| Country | Military service age and obligation |
| Guatemala | all male citizens between the ages of 18 and 50 are liable for military service; conscript service obligation varies from 12 to 24 months; women can serve as officers (2007) |
| Guernsey | void |
| Guinea | 18 years of age for compulsory military service; 2-year conscript service obligation (2006) |
| Guinea-Bissau | 18 years of age for selective compulsory military service (2006) |
| Guyana | 18-25 years of age for voluntary military service; no conscription (2008) |
| Haiti | void |
| Heard Island and McDonald Islands | void |
| Holy See (Vatican City) | void |
| Honduras | 18 years of age for voluntary 2 to 3-year military service (2004) |
| Hong Kong | void |
| Howland Island | void |
| Hungary | 18 years of age for voluntary military service; conscription abolished in June 2004; 6-month service obligation, with reserve obligation to age 50 (2006) |
| Iceland | void |
| Iles Eparses | void |
| India | 16 years of age for voluntary military service; no conscription (2008) |
| Indian Ocean | void |
| Indonesia | 18 years of age for selective compulsory and voluntary military service; 2-year conscript service obligation, with reserve obligation to age 45 (officers); Indonesian citizens only (2008) |
| Iran | 19 years of age for compulsory military service; 16 years of age for volunteers; 17 years of age for Law Enforcement Forces; 15 years of age for Basij Forces (Popular Mobilization Army); conscript military service obligation - 18 months; women exempt from military service (2008) |
| Iraq | 18-40 years of age for voluntary military service (2006) |
| Ireland | 17-25 years of age for male or female voluntary military service (17-27 years of age for the Naval Service); enlistees 16 years of age can be recruited for apprentice specialist positions; maximum obligation 12 years; 17-35 years of age for the Reserve Defense Forces; EU citizenship or 5-year residence in Ireland required (2008) |
| Isle of Man | void |
| Israel | 18 years of age for compulsory (Jews, Druzes) and voluntary (Christians, Muslims, Circassians) military service; both sexes are obligated to military service; conscript service obligation - 36 months for enlisted men, 21 months for enlisted women, 48 months for officers; reserve obligation to age 41-51 (men), 24 (women) (2008) |
| Italy | 18-27 year of age for voluntary military service; conscription abolished January 2005; women may serve in any military branch; 10-month service obligation, with a reserve obligation to age 45 (Army and Air Force) or 39 (Navy) (2006) |
| Jamaica | 18 years of age for voluntary military service; younger recruits may be conscripted with parental consent (2001) |
| Jan Mayen | void |
| Japan | 18 years of age for voluntary military service (2001) |
| Jarvis Island | void |
| Jersey | void |
| Johnston Atoll | void |
| Jordan | 17 years of age for voluntary military service; conscription at age 18 was suspended in 1999, although all males under age 37 are required to register; women not subject to conscription, but can volunteer to serve in non-combat military positions (2004) |
| Juan de Nova Island | void |
| Kazakhstan | 18 years of age for compulsory military service; conscript service obligation - 2 years; minimum age for volunteers NA (2004) |
| Kenya | 18 years of age (est.) for voluntary service, with a 9-year obligation (2007) |
| Kingman Reef | void |
| Kiribati | void |
| Korea, North | 17 years of age (2004) |