We know how age affects the brain during lab-based tasks, but what about situations truer to everyday life, such as watching movies? We measured fMRI activity while participants (N=577) from the Cambridge Centre for Ageing and Neuroscience (www.cam-can.com) watched a movie. Watching the same movie induces significant inter-subject synchronization of brain activity across participants. These cross-subject correlations suggest that viewers are processing incoming information in a similar (or shared) way. We show that with advancing age, synchrony is preserved in some areas, including the language network, but decreased in others, including the medial prefrontal cortex, medial temporal lobe and fronto-parietal network. Synchrony declines were driven by more idiosyncratic responding in older adults and were associated with regionally-distinct temporal profiles and functional connectivity patterns, as well as declines in white matter integrity. These findings suggest that areas involved in language processing remain intact with age, while regions involved in attentional control and memory may show age-related declines, even in situations similar to daily life.