Many new technologies, such as smartphones, computers, or public-access systems (like ticket-vending machines), are a challenge for older adults. In the diminished state space theory of human aging, I suggest that these difficulties emerge from an underlying deficit in the representation of state spaces of cognitive tasks. In the first part of the talk, I will explain what I mean with state spaces and will present some of the empirical findings on age-related changes in learning and decision-making that led to the state space hypothesis. This will be followed by a description of the computational and neurobiological predictions that can be derived from the theory. I will conclude with some ideas for a generalization of the state space hypothesis to other cognitive domains and with a speculation on how age-related deficits in state space representations might be reflected in age differences in neural manifolds.