This study explores the effects that the age of onset (AO) of second language (L2) acquisition exerts on the attrition of first language (L1) event conceptualization patterns. The subjects studied are L1 Spanish-L2 Swedish bilinguals living in Sweden. The specific research questions addressed in the study concern the role of AO in endpoint encoding and temporal perspectivation in goal-oriented motion events. In view of previous findings on age effects in attrition, it is hypothesized that deviations from Spanish monolingual patterns of conceptualization would be limited basically to subjects whose AO is below 12 years of age. The analyses show that subjects with AO > 12 converge with Spanish monolingual controls on both endpoint encoding and temporal perspectivation strategies, whereas deviations from the controls' performance are found exclusively in subjects with AO less than 12. It is suggested, in view of these findings, that subjects with early AO are more dependent on advantageous socio-psychological circumstances such as L1 contact and use in order to fully acquire/maintain Spanish event conceptualization patterns, while L1 maintenance in subjects with late AO is less dependent on these factors. It is concluded that patterns of event conceptualization are affected by age in the same way as formal language skills.