So Cher as Catwoman? Who sold that to a reporter? I doubt it, more from the acting side and the celebrity-bigger-than-the-film side. Actually, the idea of an older Catwoman would be the sort of creative break Christopher Nolan might well employ. It would be the ultimate roll of the cinematic dice - either unconventional and brilliant, or an everlasting punch line in the making.
If you're going older, why not Michelle Pfeiffer? Or heck, Julie Newmar? Or Sean Young. I hear she makes her own costumes.
There are plenty of fifty-something and sixty-something actresses who would be more interesting in the role. Heaven knows Hollywood grants them plenty of time on their hands.
Judi Dench. Helen Mirren. Holly Hunter. Joan Allen. Sissy Spacek. Sigourney Weaver, to name a few. Add the forties and you have Laura Linney, Diane Lane, and others that I'm not thinking of.
EDIT: A couple more .... Catherine Deneuve. She might still be able to wear the tight leather. Oh, I thought of someone else but now it's gone.