This exploratory study investigates the knowledge of word order in intransitive sentences by heritage speakers of Spanish of different age groups: 9-year-olds, 13-year-olds and adults. In doing so, we aim to fill a gap in the heritage language literature, which, to date, has mainly focused on adult heritage speakers and preschool bilingual children. The results from a judgment task reveal that child- and adolescent heritage speakers do not entirely resemble monolingual age-matched children in the acquisition of subjects in Spanish, nor do they assimilate adult heritage speakers. The data suggest that several different processes can occur simultaneously in the acquisition of word order in heritage speakers: monolingual-like acquisition, delayed acquisition, and attrition. An analysis of the influence of extraneous variables suggests that most of these effects are likely to be the consequence of quantitatively reduced input in the heritage language and increased input in the majority language.