False
Most people who join the military, do so through the Delayed Enlistment Program (DEP). They sign up, but are not required to report for basic training for up to a year after signing. During this time, many youth change their minds, and it is actually quite easy to leave the Delayed Enlistment Program.
For details, see:
www.afsc.org/youthmil/html/news/june00/askus.htmgirights.objector.org/delayed-enlistment-program.html