What does this quote mean?

If bilingualism and language acquisition/dominance effects operate across all ages, then the explanatory onus would subtly move away from biology (critical hypotheses) and on to changes in the brain and in cognitive processing that are shaped by the experience that results from being exposed to more than one language simultaneously or sequentially and across varying ages.  The punitive impossibility to attain nativelikeness after a certain age, if reinterpreted under a bilingual lens by SLA researchers themselves, may turn out to mean that it is impossible for bilinguals to be monolinguals.