To alleviate the impacts of an aging society, developing age-friendly cities has become an urgent agenda for governments around the world. The World Health Organization proposed a number of features of age-friendly cities in Global Age-friendly Cities: A Guide in 2007 that were based on eight aspects of aging societies. Based on these features, the Nantou County Government implemented a certification program for age-friendly tourism shops and hotels in 2013. This study investigated problems arising from the implementation of the certification program in Nantou County. By literature review and expert questionnaire of modified Delphi method, a set of key factors (major and minor factors) was constructed and verified. Subsequently, the relevance and significance of the major factors were analyzed using the decision-making trial and evaluation laboratory (DEMATEL) method, and the weights of the minor factors were computed and sorted by the analytic hierarchy process (AHP). After being extracted from a literature review and verified by 17 experts, four major factors and 18 minor factors were identified. The results of the DEMATEL analysis reveal that, ＂environment safety＂ is the pivotal major factor that influences all other major factors and ＂quality of service＂ is the major factor that is most susceptible to influence from other factors. The results of the AHP analysis indicate that in major factor ＂quality of service＂ facet, ＂providing prioritized and on-time service to the elderly＂ is the most critical factor; in ＂environment safety＂ facet, ＂nonslip facility＂ is the most critical factor; in ＂healthy diet＂ facet, ＂low fat, low sugar and low salt＂ diet is the most critical factor; and in ＂recreational activities for the elderly＂ facet, ＂transportation and tourist information＂ is the most critical factor. Based on these results, a mind mapping decision model of this study was completed and shown by a mind map.