Although the health benefits of physical activity (PA) are well-established, the prevalence of insufficient PA among older adults is alarmingly high and points to a considerable scope and need for improvement. Research is urgently needed to identify modifiable aspects of the neighbourhood that may be entry-points for interventions to make environments more conducive to PA for older adults. This project aims to overcome earlier methodological limitations and gain novel insights on environmental determinants of PA in old age. We propose that walkability is a crucial environmental construct for older adults’ PA. In our project, we will combine fine-scale spatial data from different geo-data sources to create walkability measures for various years and personalized exposure areas covering the whole of the Netherlands. We will link these objective measures to PA-data of older adults from the Longitudinal Aging Study Amsterdam. We will then (a) examine associations between changes in walkability, and its components, with changes in PA, and (b) assess whether these associations differ by individual characteristics and contextual conditions. The findings will offer perspectives to policymakers, urban planners and public health professionals on how to optimally design neighbourhoods to increase older adults’ PA, which subsequently will promote active and healthy aging.