A life-course approach to enhance tolerance to and prevent dementia and senescence is increasingly embraced by scientists, clinicians and policy makers to promote healthy ageing. Tolerance enhancement and prevention remain the most sensible courses of action given the lack of effective dementia treatment. We discuss the modifiable risk factors of dementia, and address social isolation and loneliness in view of their importance from a psychological and societal perspective. The effectiveness of prevention strategies and non-pharmacological intervention is increasingly supported by scientific evidence. They support an actionable model of dementia and senescence prevention that is cost effective and converges with established public health programmes (diet, exercise, mental health). They also relate to central societal issues (social inequality, pollution, healthcare), and translate to multidisciplinary professional interventions that are tailored to the individual. Changing lifestyle might be an effective way to address the challenges of dementia and senescence in our ageing populations, but also represents one of the most formidable psychosocial and societal challenges.