Aged population is growing rapidly and aging in place is the major endowment pattern for older people. This study focused on the thermal living environments and thermal comfort of older people in their own homes. Special attention was paid to their behavioral adjustment characteristics. The longitudinal investigation was conducted from March 2018 to March 2019 in a residential community in Beijing, China, and the participants involved 5 households with 10 older respondents. The investigation included a yearlong continuous environmental measurement, behavioral monitoring, and a monthly collection of subjective evaluations. Face-to-face interviews on behavioral adjustments were also conducted with 102 older respondents in different communities in Beijing. The field investigation involved the observation of seasonal variation in the indoor environments and subjective evaluations. The prediction accuracy of the predicted mean vote (PMV) model was found to be inconsistent for thermal sensations of older people between the cold side and hot side. With regard to the behavioral adjustments of older people, this study described the effect of the outdoor temperature on window opening behavior and air conditioner use, and the effect of indoor temperature on clothing behavior. The preference for the adjustment methods were studied, and the personal characteristics of older people (including sex, age, educational background, and time spent at home) were found to influence their preference for different methods. The differences in behavioral adjustments between older and non-older people and between older people in different climate zones were discussed by comparing this study to previous field studies.