Global population ageing has escalated the burden of chronic diseases, driving a paradigm shift from treatment centered medicine toward preventive, personalised health management. Artificial intelligence, wearable sensing, and big data analytics offer unprecedented opportunities to integrate nutrition, exercise physiology, gut microbiome science and real world service delivery. This study synthesises multidisciplinary evidence to construct a holistic AI driven personalised health management framework covering nutritional metabolism, gut brain axis mechanisms, evidence based dietary patterns, exercise physiology for healthy ageing, and digital health industrial practices. We systematically reviewed the performance of image based dietary assessment, personalised nutrition recommendation algorithms, AI posture recognition for physical training, and closed loop monitoring via wearable physiological data. Key findings indicate that gut microbiota acts as a critical biological mediator linking diet, lifestyle and chronic disease risk. Customised multimodal AI models achieve acceptable accuracy for dietary evaluation, while AI virtual coaching systems enable safe home based exercise, particularly for older adult populations. Nevertheless, critical gaps remain, including insufficient long term user retention mechanisms, safety risks for AI generated exercise advice, and misalignment between regulatory frameworks and fast evolving digital health technologies. Furthermore, this work proposes multi category business models and a cross sector health ecosystem spanning consumers, healthcare providers, food supplement industries and technology vendors. The framework provides technical, clinical and industrial references for advancing preventive personalised healthcare and healthy ageing interventions.