One of the reasons that elderly people like keyboard shortcuts is because learning how to use a mouse can be quite difficult, as it requires precise hand-eye coordination (which is also why it's slow, causing techies to rely on the keyboard as much as possible). At that age, not only is it difficult to learn how to operate new devices, but their afferent & efferent neurons may not be up to the task to begin with.

Yup. When my mom tries to double click a mouse button, I hear anything from two to five clicks, and the mouse shudders under her hand as she attempts this. The result is predictably unpredictable. She seems to do OK with single clicks.