Jakob Nielsen weighs in on usability for seniors:

“Websites tend to be produced by young designers, who often assume that all users have perfect vision and motor control, and know everything about the Web. These assumptions rarely hold, even when the users are not seniors. However, as indicated by our usability metrics, seniors are hurt more by usability problems than younger users. Among the obvious physical attributes often affected by the human aging process are eyesight, precision of movement, and memory.”