You can get chaptered out for not meeting height/weight requirements, repeated failures of PT tests, you can get an Article 115 separation for malingering/failure to adapt, you can get a medical chapter if you have or develop a medical condition which prevents you from performing your assigned functions, or you can go the criminal route, which would result in an Other-Than-Honourable or Dishonourable Discharge.
Army
Enlist or Enlistment
18
joining the military
until your enlistment expires
enlisted personnel must service out their enlistment unless there is a dire cause for early release. An officer can resign from service..............
The age limit for women in the military varies depending on the country and the specific branch of the military. In many countries, there is no specific age limit for women in the military, and they can serve as long as they meet the physical and medical requirements. It's best to consult the specific regulations of the country and branch of military you are interested in for accurate information.
The foreign legion
The U.S. Army websites provides the oath of enlistment and details about the oath. Websites such as Wikipedia, Military, and wiseGEEK also provide information about the oath of enlistment.
You can get you license while serving in the military, however you will have to have a State Issued Identification Card prior to enlistment, now the military will not issue you a license you will still have to go through the State. Keep in mind certain jobs require a license prior to enlistment.
DFAS
The Department of Defense restricts enlistment into the military to People ages 35 or younger. You can re-enlist at a later age if you have prior year's service to apply to the enlistment cutoff.