Most military programs accept applicants as young as 17. The Army requires parental permission to join, and the Navy and Air Force require applicants to be at least a senior in high school with plans to graduate, while the National Guard requires applicants to be at least 17 years old and a junior. The service provides extensive benefits for recruits. For example, as long as someone lives on base, housing, medical and dental bills are all paid for. If a recruit has a spouse, he or she enjoys the benefits too.
Air transportation is free.
In addition, there is usually a signing bonus ranging in value for those who enlist. There are college opportunities in all of the services. Skills learned throughout training can earn a recruit college credits that can go towards a degree or be transferred to other colleges after leaving the service. I know that as long as I keep in touch every once in a while, I could depend on my buddies if I should ever need them. Service terms range from two to six years, but as long as a person is still capable of performing a job to the expectations of the service, there's no real age limit.