The Spartan IIIs were 13 in ghosts of onyx, but they are 18/19 now.
It wasn't the thinness that made me think female, but the shape of the body. Not may guys have waists narrower than their hips. Anyway, it's moot. It's just artwork. We know it isn't a girl now. I need more info!!!
The sad thing is we might not get any until next year's E3