Psychological distress in cancer patients is inversely related to age, although the reasons are unclear. The adult development literature suggests that ageing may be associated with the development of adaptive capacities, specifically greater attachment security (the sense that others will be available and supportive when needed) and spirituality (the capacity to view one's life as having meaning, purpose and value), that enable older people to cope better with disease. We examined whether age-related patterns in attachment security and spiritual wellbeing account for the protective effect of age against distress. Measures of depression, attachment security, spiritual wellbeing and disease burden were collected from 342 patients aged from 21 to 88 years with advanced, metastatic cancer. Attachment security and spiritual wellbeing were tested as mediators of the effect of age on depression, controlling for disease burden. It was found that age was associated inversely with depression and positively with spiritual wellbeing and attachment security. Depression was inversely related to attachment security and spiritual wellbeing, and the effect of age on depression was fully mediated by attachment security and spiritual wellbeing. The relative protection from psychological distress among older cancer patients may be the result of age-related developmental accomplishments and/or differences in the response to adverse life-events.