Due to increased life expectancy and decreased fertility rate, the proportion of elderly population has risen in developed and industrialized countries. This increase in aging population has drawn global interest to aging issues. However, despite active research on this issue, the following problems remain. Firstly, research on ways to familiarize senior citizens with smart devices is lacking. Secondly, research on consumption of digital contents among senior citizens using smart devices is also lacking. For senior citizens to utilize and get the best of smart devices and digital contents, focus must be placed on usability and their familiarity with smart devices. In this paper, we propose a cognitive reaction-based intelligent UI/UX system that provides UI/UX optimized for senior citizens based on the user's cognitive functionality and activity log. With this work, we expect improvements in the usability of smart devices among senior citizens and in their life quality, by personalizing content and experience for the user. Furthermore, improvement in social perception by the general population can also be anticipated, thanks to familiarity with smart devices provided by this system.