A lot of people have said "rides for seniors don't have to be boring, enough with the sitting on the bench stuff!" And I agree with this, however here are the criteria that I use for thinking about what's good for a senior, add any you guys can think of:
1.) Capacity for a longer attention span.
2.) More interested in history/nostalgia.
3.) Less banging you up. Not as much of a concern in Disney as in some other parks.