earlier onset age) helps to develop learners' intuition about its grammatical rules, syntax, phonology, and more (Schouten, 2009;Newport et al., 2001;Johnson and Newport, 1989;etc.).
many researchers question it because there is a lack of consensus about the biological underpinnings of the theory, and much of the supporting research is contradicted by other studies or can be explained by a number of other factors (see Strid, 2017 for an in depth review).