This study gathered information from 120 volunteers. Some of them began learning English in kindergarten or grade one, while others didn't start until grade four or until they were in secondary school. Both quantitative and qualitative methodologies were used in the investigation. Date was analyzed using means, standard deviations, ANOVA and multiple comparison in SPSS. Structured interviews were conducted to articulate how the age of onset influenced English capacities and how other possible factors operated in the process of learning. This study provides a thorough grasp of the “crucial period theory” by elucidating the impact of starting age on various English skills. According to the findings, it is important to begin teaching English in the lower and intermediate classes of elementary school. Nevertheless, there will always be discoveries about how people learn languages. (Mokwon University)