Nielsen Norman GroupEvidence-Based User Experience Research, Training, and Consulting
Users aged 65 and older are 43% slower at using websites than users aged 21–55. This is an improvement over previous studies, but designs must change to better accommodate aging users.
If using web or browser-related terms, consider defining them in place to make websites easier for senior citizens. Avoid using technical words if they are not necessary.
A strict focus on accessibility as a scorecard item doesn't help users with disabilities. To help these users accomplish critical tasks, you must adopt a usability perspective.
Lower-literacy users exhibit very different reading behaviors than higher-literacy users: they plow text rather than scan it, and they miss page elements due to a narrower field of view.
The key difference between user interfaces for sighted users and blind users is not that between graphics and text; it's the difference between 2-D and 1-D. Optimal usability for users with disabilities requires new approaches and new user interfaces.