© 2020 Walter de Gruyter GmbH, Berlin/Boston. Research on age and second language acquisition (L2A) is vast, but inconclusive. Such research has mainly been motivated by the Critical Period Hypothesis (CPH), which postulates that language acquisition becomes extremely difficult after the onset of puberty. Also, there is a lack of research on age and third/additional language (L3/Ln) learning. To fill this gap, this article examines differences in morphosyntactic knowledge between early and late learners of English as a L3/Ln. In this study, 'early' and 'late' learners are those participants first exposed to English as a medium of instruction (MOI) in 1st and 11th grades, respectively. Participants' morphosyntactic knowledge was assessed based on two tasks: (a) a Grammaticality Judgment Task (GJT) and (b) an editing task. Three hundred and thirty five undergraduate and graduate students from two universities in Pakistan voluntarily participated in the research. Results of the group comparisons showed no statistically significant differences between early and late learners on the GJT; however, on the editing task, a modest but significant difference was observed between the two groups, with late learners scoring higher. This finding contradicts the predictions of the CPH.