Neurodevelopmental origins of functional variation through the lifespan are increasingly acknowledged. Evidence converges on early life factors being important for both normal individual differences in adult brain and cognition and risk of developing neurodegenerative disease in old age. As much evidence points to factors from early life stages being important, we need to investigate to what extent these are genetic and environmental, and how cognitive functioning can be impacted at different ages. This is critical, as possibly stable individual differences in how our brains adapt to the environment lay at the heart of understanding lifespan changes in cognition.