Design an app or website for older adults, children, or other specific users

Help me design an interface that works well for a specific group of users. Product and main tasks: [e.g. "telehealth app: book appointments, join video calls, message the clinic"] Primary user group: [e.g. "adults over 70", "children aged 6-9", "people with low literacy", "field workers wearing gloves", "first-time smartphone users"] What I know about them: [research findings, abilities, devices, contexts of use] Platform: [mobile app / web / kiosk / tablet] Current design or problems: [DESCRIBE or paste screenshots, or "new design"] Give me: 1. What's different about this group: their likely needs and constraints in vision, motor control, reading, memory, attention, tech confidence, and context. Separate well-established findings from assumptions I should test. 2. Design principles for this group, each with a concrete rule (e.g. minimum touch target size, text size and contrast, number of steps per task, use of icons with labels). 3. Guidance on navigation, forms, error messages, onboarding, and feedback for my main tasks. 4. Content and tone: reading level and wording that respects users (no talking down). 5. Pitfalls specific to this group, such as gestures they may not discover, timeouts, or dark patterns that hit them harder. 6. Accessibility: the WCAG criteria most relevant to this group. 7. If I shared a design: specific problems and fixes, ranked by severity. 8. A test plan: how to recruit participants from this group, 5 tasks to test, and what to measure. Include consent steps, and parental consent for children. Don't treat everyone in a group as the same; design for the range of abilities within it.