We examined how age of acquisition in Spanish heritage speakers and L2 learners interacts with implicitness vs. explicitness of tasks in gender processing of canonical and non-canonical ending nouns. Twenty-three Spanish native speakers, 29 heritage speakers, and 33 proficiency-matched L2 learners completed three on-line spoken word recognition experiments involving gender monitoring, grammaticality judgment, and word repetition. All three experimental tasks required participants to listen to grammatical and ungrammatical Spanish noun phrases (determiner–adjective–noun) but systematically varied the type of response required of them. The results of the Gender Monitoring Task (GMT) and the Grammaticality Judgment Task (GJT) revealed significant grammaticality effects for all groups in accuracy and speed, but in the Word Repetition Task (WRT), the native speakers and the heritage speakers showed a grammaticality effect, while the L2 learners did not. Noun canonicity greatly affected processing in the two experimental groups. We suggest that input frequency and reduced language use affect retrieval of non-canonical ending nouns from declarative memory in L2 learners and heritage speakers more so than in native speakers. Native-like processing of gender in the WRT by the heritage speakers is likely related to context of acquisition and particular experience with oral production.