This study proposes a new methodology for addressing the gap between smart city technologies and their ability to inform policy making. Utilizing a digital twin city in the context of participatory design thinking, the protocol developed here consists of five milestones that facilitate joint decision making in realms of urban welfare such as urban aging. This protocol meets the world of urban governance at a time when cities are facing vast and complex issues, offering cities and neighborhoods a methodology that enables them to embrace digitalization and data-based decision making. This, in turn, stands to enhance their ability to contend with and manage the complex realities of the city. The methodology ranges from a generic protocol, which  can be adapted in a variety of contexts, to our specific case study of urban aging