Age effects in “returnee” bilingualism : Problematizing their conflation as prima facie evidence for linguistic maturation

The keynote article, What returnee bilinguals may teach us about language attrition, language stabilization and individual variation by Flores and Snape (2025), henceforth F&S, takes the reader through a full-bodied and thought-provoking accounting of the linguistic trajectories of "returnee bilinguals" (RBs)-individuals who, after spending formative years "abroad" in linguistic immersion of a distinct societal language, return to their (family's) country of origin.While work on RBs has increased in recent years, it remains understudied and, thus, for some readers the very construct of RBs as a distinct type of bilingual will be entirely new.With this in mind, F&S do a service to the broader field via a stellar summarizing and framing of the questions posed as well as the available data and argumentation drawn from them in this growing literature.Moreover, they highlight and critically evaluate the many opportunities that research in the unique, naturally occurring RB laboratory affords for addressing long-standing theoretical and practical issues in the language sciences.To be sure, there is much to be applauded in F&S's coverage and discussion.As to be expected, there is, nevertheless, room for query with the goal of clarification and, thus, maximization of the potential contribution epistemological work such as this can have.Drawing from empirical and longitudinal studies, F&S explore four research themes: (1) the role of age and maturation in language attrition, (2) the contribution of returnee research to modelling individual variation, (3) the vulnerability of different linguistic domains to attrition, and (4) the potential for language re-stabilization.Each of these themes can and should be commented upon, as no doubt colleagues will do in their commentaries.Given space limitations, we focus solely on theme (1) where issues worthy of serious theoretical pondering, in our view, arise from F&S's argumentation.Our query relates mainly to the very notion of maturation itself, with trickle-down effects for RB evidence specifically and for language acquisition/processing more generally.More precisely, we query whether work from RBs can truly provide insights for long-standing debates related to so-called linguistic maturation?If so, in what ways?Concentrating our discussion on this aligns well with the overall focus of F&S on the attrition of the early-acquired diasporic majority language after return migration, especially when this language is no longer reinforced in the return context.In line with Schmid & Köpke (2017), F&S define attrition as a decline in language skills due to reduced use and conceptualize it as part of a continuum of bilingual development.F&S argue that RBs are ideal for studying attrition because their shift from high to low input typically occurs suddenly and completely, offering cleaner starting points for investigating change.There is no doubt that RB research documents novel, asymmetric trajectories in attrition patterns that (tend to) correlate to age.In this respect, we concur that RB data embody otherwise missing observations that should be considered and shed some novel light on attrition proper.However, it is not clear to us how RB data provide unique, much less maximally relevant data specifically for linguistic maturation per se, which we will spend the remainder of our commentary contextualizing.Let us begin with a summary of some particularly pertinent observations that F&S demonstrate.RB findings show that children who return before puberty are especially vulnerable to rapid attrition, particularly in lexical retrieval and morphosyntactic domains.This is supported by case studies F&S detail, showing sharp declines in productive skills within