Since I've mostly explained the races that dwell in Starcademy thusfar, this won't be too long... I hope. :D
Anyway, Starcademy came about some three or four generations ago, after Earth first made contact with the Rigelians. The Rigelians had intercepted Earth's Voyager spacecraft, and, following the directions upon it, made their way from their wartorn galaxy to the Sol System, where they encountered Earthers for the first time.
Shortly after, they formed 'Several Tough Alien Races Defense-Only Guarding Space', henceforth known as the STARDOGS.
In order to train young cadets, the Starcademy was built, which admitted all of the Rigelian and Earther cultures, including humans, Saturnians, Uranusians, and Mercurians... And, more recently, it has started accepting Andromedans, and the occasional Spung that wishes to break away from Kjkk.
Cadets are trained from a young age - twelve for Earthers, nine for Saturnians, and as young as seven for Mercurians and Uranusians, who tend to mature faster than Earthers. They learn not only academic subjects, but when they reach college age, they also major in a particular area. In addition to that, they are also trained in combat situations. Students are discharged around age twenty-three, when they enter a tenure of active duty in the military.
...See? That wasn't so bad. :D