In Eden, the Military could start recruiting from a young age, perhaps as early 12 years old. However, they naturally weren't sent to wars or anything like that. Rather, there was a military academy they would attend.
It'd teach the normal subjects through high school, but also dedicate a lot of units to military subjects like combat basics, physical conditioning, strategy, logistics management, and so on.
Anyway, compared to normal high school, the students' lives pretty much revolved around the school. There were also a few years wherein they'd be required to use the dormitory even if their houses were nearby.
That said, all military personnel in Eden were guaranteed decent lives. They'd have food, shelter, salary, and pension. At the time, his impression was that he could be paid for fighting, which he was in a sense.
