This study addresses the question of how age of acquisition (AoA) affects grammatical processing, specifically with respect to inflectional morphology, in bilinguals. We examined experimental data of more than 100 participants from the Russian/German community in Berlin, all of whom acquired Russian from birth and German at different ages. Using the cross-modal lexical priming technique, we investigated stem allomorphs of German verbs that encode multiple morphosyntactic features. The results revealed a striking AoA modulation of observed priming patterns, indicating efficient access to morphosyntactic features for early AoAs and a gradual decline with increasing AoAs. In addition, we found a discontinuity in the function relating AoA to morphosyntactic feature access, suggesting a sensitive period for the development of morphosyntax.