The oldest gamer I know is in his middle 60s. He is an exceptionally talented tank whose well above average environmental awareness probably has something to do with his two tours in Vietnam with the Marines.
MMOs have immense untapped potential to not only entertain but to enhance quality of life for seniors. Wire up our old-age homes and instead of warehousing old folks and drugging them into submission, give them keyboards and let them live new lives where they can run, fight, adventure and yes -- fool around, independent of their failing bodies.
The spirit and compassion of your idea is not lost on me. However, I have a terrible image in my head of abusive and self serving nursing home staff forcing the elderly to farm gold 18 hours per day.