The importance of age effect on an additional language (L2) acquisition has long been recognized in the field of L2 education. Research was conducted to reveal the influence of age to the rate and ultimate attainment of L2 teaching and learning, yet controversial results were discovered. Consequently, stereotypes and misunderstanding exist among educators, practitioners, parents and/or guardians, which may affect students' L2 learning. This article reviewed the significant studies in the past and discussed the current agreements and debates around the age effect on L2 acquisition. It provides a comprehensive overview of the topic that is beneficial for L2 education. The author proposed that more contributions are needed to provide additional evidence to explore this issue.