They are not old, at all for pairs. I knew they were young, in Turin, with that freak fall, when they made headline, i thought it was a known fact that they were harly 20+.If they are only injured, most likely they will continue, China has no world class level pair beside Pang / Tong at the moment, and thay are around 30 so most likely they won;t be around many years from now. Zhang's should be still young enough in 2014, by that time, they could evolve artistically, if they would work with the right choreographer.
S/Z and P/T were not artistical skaters in their early career either, but look how far trhey have come, once they put emphasis on the artistry. It's possible.