Answer:
To join the U.S. military, non-citizens must be living permanently and legally in the United States. Non-citizens must also have permission to work in the United States, possess an I-551 (Permanent Residence Card), have obtained a high school diploma and speak English
The minimum age for enlistment in the Army is 17 years with parental consent or 18 years without parental consent. Under federal law, the oldest recruit any military branch can enlist is 42. Even so, each branch of the U.S. military may set their own policy below that age limit for applicants seeking to enlist.