In Thailand, rapid demographic ageing is closely linked to an increased incidence of non-communicable diseases (NCDs). Effective nutritional management is essential to mitigate NCD risks and delay progression. Given the widespread use of touchscreen devices among older adults, this study focused on developing a nutrition app tailored to enhance knowledge, attitudes, and practices regarding healthy eating among Thai elderly people. Methods: The project consisted of two main phases, namely content preparation and application development. Initial drafts and storyboards were refined through consultations with experts and discussions. The use of healthy menus was approved by a professional chef and nutritionists. The app prototype underwent comprehensive evaluations in terms of content accuracy, design, usability, and acceptability by experts. It was also field tested by elderly volunteers for four weeks. Results: The developed “YoungYou” app features tools such as body mass index assessment, updates on elderly health, and dietary recommendations tailored to Thai elderly individuals based on the nutrition flag system. It includes 60 healthy recipes, 30 cooking tutorials, and an interactive community board. The app allows users to modify and recalibrate the nutritional content of recipes, which can then be saved or shared. Evaluations of the app showed high levels of agreement on its effectiveness across all metrics. The use of rice, vegetables, and meat by 41 elderly volunteers led to increased healthy eating behaviours. Conclusion: The “YoungYou” app has demonstrated potential as a viable tool for promoting healthier eating habits among Thai elderly people, thereby addressing critical public health issues related to ageing and disease prevention.