Impulsivity is often characterized by rapid decisions under risk, but most current tests of decision-making do not impose time pressures on participants' choices. Here we introduce a new traffic lights test which requires people to choose whether to program a risky, early eye movement before a traffic light turns green (earning them high rewards or a penalty) or wait for the green light before responding to obtain a small reward instead. Young participants demonstrated bimodal responses: an early, high-risk and a later, low-risk set of choices. By contrast, elderly people invariably waited for the green light and showed little risk-taking. Performance could be modeled as a race between two rise-to-threshold decision processes, one triggered by the green light and the other initiated before it. The test provides a useful measure of rapid decision-making under risk, with the potential to reveal how this process alters with aging or in patient groups.