In the US, there is no mandatory service requirement. You are, however, required to sign for the Selective Service Act when you turn 18, which makes you eligible for mandatory service, should the draft be reinstated.
Some countries do have a mandatory military service requirement. See related link "Wkipedia.org - Military Service" for a listing of these countries.
In most countries, enlisting in the military is not mandatory. However, there are countries with mandatory military service laws that require all eligible citizens to serve in the military for a specified period. It's important to check the requirements and laws of your specific country to understand if military service is mandatory or voluntary.
In all states, parental consent is required before a minor can enlist in the military. How does a parent revoke his/her consent?
A GED or High School diploma is required to enlist. At one time, many people (including me) DID earn their GED while serving in the military.
17 with a parents approval.
Enlist in the military.
check with a military recruiting office
Enlist or Enlistment
If the military is aware that you have been formally diagnosed with a personality disorder by a qualified, licensed mental health professional, then it is unlikely that you will be able to enlist.
Conscription.
This depends on the country that you live in, whether mandatory HIV testing is required to enlist, and whether a positive result is an exclusion to serving. In some countries this is no in other it is yes.
Go enlist
A veteran is someone who's done things before, and you usually enlist in the military. A good sentence would be "The veteran wanted to enlist again, but was too old."
ask a recruiting officer