If Cluxton looks after himself, which I’m sure he does, and is lucky with injuries, which he seems to be, he could play to his late 30’s if he wished.
I’m less worried about Cluxton packing it in than getting an injury. The understudy needs time. It’s an unique position as described above but you’ve also no choice if your first choice gets injured. Your left with a guy with zero big match experience in a key position. That’s un Gavin like in many ways.