This paper investigates gender agreement mismatches between nominal expressions and the targets of agreement they control in two groups (adults and adolescents) of Heritage Greek speakers in the USA. On the basis of language production data elicited via a narration task, we show that USA Greek Heritage speakers, unlike monolingual controls, show mismatches in gender agreement. We will show that the mismatches observed differ with respect to the agreement target between groups, i.e., noun phrase internal agreement seems more affected in the adolescent group, while personal pronouns appear equally affected. We will argue that these patterns suggest retreat to default gender, namely neuter in Greek. Neuter emerges as default when no agreement pattern can be established. As adult speakers show less mismatches, we will explore the reasons why speakers improve across the life span.