I'm pretty sure all the fretting over him playing a Terminator is without merit. For all we like to slag off Hollywood and lament its lack of originality and good ideas, I'm pretty sure even they're not stupid enough to think a 70-year-old Terminator is going to fly with anyone.
On the other hand... a Terminator's flesh hull was supposed to get old, too. It's a machine underneath, right?
I don't recall them ever saying specifically that the flesh would age, just that it would sweat, bleed, heal minor wounds...etc. I suppose it's possible though.
Still think it would make more sense to have him as the basis for the design. Maybe a captured resistance hero that they try and replace to subvert the resistance from within, and just end up keeping the template for further models.