Ok, so my character could have been a test pilot for Aegisframes, and when he proved himself, transferred to Advent Horizon?
Aegisframes are very, very rare, so it's unlikely that he'd have been able to test one. Rather, he'd likely be testing normal Warframes, and at some point, would feel a connection with an Aegisframe (As if drawn to it, without ever having seen one or being near one). And when those in charge found out he had somehow formed a bond with an Aegisframe, he would have pretty much immediately been put into training on it.
Sort of a... The Wand Chooses the Wizard, only in this case, it's giant robots.
I'd say that's the only thing that should be changed on the sheet is that he'd be a test pilot for Warframes in general, but only be allowed even near an Aegisframe, or even allowed to know their existence, once he felt the call of one.