Arsenio's an Ensign at 16? Rich is only a Sergeant First Class at 22. Using the real-world as a guide, most make Ensign at 25 on average. Here's Orb's military rank structure: 

[quote][u]Commissioned Officers[/u]
Admiral
Rear Admiral
Captain
Commander
Lieutenant Commander
Lieutenant
Lieutenant Junior Grade
Ensign

[u]Noncommissioned Officers[/u]
Sergeant Major
Master Sergeant/Sergeant 1st Class/Sergeant
Leading Private
Private 1st Class/Private/Recruit[/quote]

EDIT
Nevermind, I guess as an Extended subject, he can jump through some holes in military norms, like Kira did.