Early foreign language (FL) programmes have grown rapidly worldwide in the past two decades, resting on the assumption that "earlier is better" for learning a FL. However, the majority of empirical studies that investigated the "earlier is better" hypothesis were conducted in naturalistic immersion contexts. Given the substantial differences in the quality and quantity of input and instruction, whether or not the results in immersion contexts can be generalised to FL learning contexts remains unknown. The current study aimed to fill this gap by reviewing and synthesising 42 empirical studies published in the past 50 years that examined the age of learning effect in FL learning contexts. Overall, the synthesis revealed no solid evidence for a younger learner advantage in short-term or long-term linguistic outcomes. We conclude with implications for research and practice.