The mezzo-soprano may be the most durable of all operatic voices, and some mezzos keep singing, and more or less
thriving, into old age. (Maureen Forrester comes immediately to mind.) Others choose not to.Frederica von Stade, arguably the greatest American mezzo of her generation (she's 65), has chosen to join the ranks of retirees while still in fine voice. The New York Times' Anthony Tommasini reviews her farewell concert on April 22 at Carnegie Hall:
http://www.nytimes.com/pages/arts/music/index.html