Younger and older adults differ in their risky choices. Theoretical frameworks on human aging point to various cognitive and motivational factors that might underlie these differences. Using a novel computational model based on resource rationality, we find that the two age groups select qualitatively different strategies. Importantly, older adults did not use simpler strategies than younger adults, they did not select among fewer strategies, they did not make more errors, and they did not put more weight on cognitive costs. Instead, older adults selected strategies that had different risk propensities than those selected by younger adults. Our modeling approach suggests that rather than being a consequence of cognitive decline, age differences in risky choice seem to mainly reflect motivational differences between age groups.