Bishop models have no reason to use organic skin (David 8 didn't). There isn't any reason they would biologically age.
There are always other ways around it, though. As I say, it could be he uploads to an intact, yet cosmetically trashed version, so that the character either sports the kind of prosthetic damage Hicks would have or covers most of the face up with a scarf or helmet or something. Both of those options would be cheaper than using CGI for every single frame of film he's in (although, in fairness, they did it reasonably well for Anthony Hopkins and Michael Douglas, so it's possible if the will is there).
Alternatively, it could be that there's a Bishop model which is deliberately designed to look older, maybe for assisting or befrinding the elderly or something. Again, Bishop could upload into one of those (or simply play one which accessed the original Bishop's data files).
When a character is AI, there are ways and means of simply 'reincarnating' them into a different body. It's just a matter of copying data over. Bishop could be uploaded into a non-humanoid form (including a tablet computer) or even a robotic body which looks female and it would be completely plausible to play out.
Interestingly, Blomkamp actually played around with that very story-telling method in 'Chappie', which means he's perfectly capable of doing it that way.