The aging population faces challenges in adopting smart wearable health devices due to usability barriers. This study aims to develop an age-friendly interaction framework that enhances accessibility, usability, and user engagement. A mixed-methods approach was adopted including observational studies, stakeholder interviews, and quantitative surveys. Observations were conducted both in-store and at home to understand user behavior and challenges in context. In-depth interviews with caregivers and sales representatives provided further qualitative insights. Finally, a survey involving 77 elderly users was conducted to evaluate 16 different interaction modalities. The findings highlight the superiority of tactile interactions over auditory, visual, and kinaesthetic modalities in terms of frequency of use, contextual richness. Based on these insights, four key design principles, validated by cognitive walkthroughs, were established: multi-modal sensory compensation, synchronized feedback, real-time validation, and emotional engagement. This study proposes a framework for designing age-friendly smart wearables that improve usability and user satisfaction.