Physical activity is considered a critical component of healthy ageing. This study aims to promote physical activity among older adults. Some efforts have been made on this topic: however, the current model is too simplified to address the complex real-life situation. An ethnographic study including participatory observation and semi-structured interviews was conducted to enhance the current empirical model. The enhanced empirical model integrates an internal system with three layers, characteristics, adaptation, and fulfilment, to describe individual attributes and an external system divided into trigger and support to address environmental influences on behaviour sustainability. Actionable guidance for both older adults and activity organisers is proposed based on the refined empirical model. Future research could consider applying the guidance in interventions to evaluate its effectiveness.