How old do you have to be before you qualify for military service?
Eighteen on your own or seventeen with parental consent (mom or dad has to sign for you.)
The maximum age of enlistment depends upon the branch of service, and if you have previously served before. Currently for first time enlistees the highest age limit is 40 and is for the Army only. Reenlisting in the military follows a much stricter guideline but may allow you to reenlist up to 54 years of age.
They simply feared induction into the military, and if they were too old for military service or otherwise unqualified for service (or had already served, thus being veterans) then they feared for their nephews, sons, grandsons, cousins, younger brothers, best friends, etc. being drafted into military service. This is why they wanted the war to end.
The military status has no effect on the "dating" arrangement between the two parties. If the question is meant to be about the legality of the two engaging in sex - the 17 year old is still a minor and under the care and legal control of her parents or guardians. Proceed with caution, especially since the service member is under the authority of two justice systems, civilian AND military.