This study investigates whether age of onset of bilingualism has an effect on ultimate attainment, and documents incomplete acquisition and attrition of tense/aspect morphology in Spanish. A group of 20 monolingual Spanish speakers, 31 US-born bilinguals, and 8 Latin America-born bilinguals participated in the study. Sixteen of the US-born participants were simultaneous bilinguals who had been exposed to Spanish and English from ages 0 to 3, the remaining 15 learned English between ages 4 to 7 (early child L2 learners), and the Latin-America-born bilinguals learned English between 8 and 12 years of age (late child L2 learners). Results of an oral production, a written completion, and two meaning-interpretation tasks showed that the simultaneous bilingual and the early child L2 groups differed significantly from monolingual Spanish speakers, while only a few individuals in the late child L2 group showed erosion with some aspects. Results suggest that morpho-phonological spell-outs and semantic features of functional categories are affected by incomplete acquisition and language loss, and that many of the patterns of divergence found resemble stages of second language acquisition.