I understand your age complaint but then we have Ana and Stephanie, who both look MUCH MUCH older than Lea does. And Lea's just too darn cute to play the part too old.
I at first didn't think that she could, but now that I think about it, I think it would be a good part for her. If you listen to some of her concert belty stuff, it's VERY good. Her voice has matured a lot since her Miss Saigon/Les Mis days and she can do a lot more with her voice (she was basically untrained when Miss Saigon happened). I've been impressed with her even more lately than I used to, and I love that woman with all of my soul.
But Glinda would be silly. Not because of singing (she could totally sing the role...but so could a lot of people, it really isn't that hard of a role to sing) but it's not exactly her acting style.
-Anyone want to turn anarchist with me?"Bless you and all who know you, oh wise and penguined one." ~YouWantItWhen????