It has been suggested that tense and aspect distributions are very difficult to learn in a second language (L2), they are prone to fossilize universally, and their interpretive properties are subject to a critical period (Coppieters, 1987). This study focuses on the acquisition of the semantic implications of the preterite-imperfect contrast in Spanish by English-speaking individuals of very advanced proficiency in Spanish who were not living in a Spanish-speaking country. By assuming that aspect is encoded in a functional category where the features [+/-perfective] are checked, depending on the language (Giorgi & Pianesi, 1997), this study asks whether ultimate attainment in the aspectual domain is possible and whether features of functional categories not selected in early childhood are subject to a critical period, as Hawkins and Chan's (1997) Failed Formal Features Hypothesis states. Experimental evidence from two tasks probing the interpretations of perfective and imperfective aspectual forms in Spanish suggests that many learners (almost 30%) in our total subject pool (including advanced to near-native speakers) and 70% of the near-native group performed like native speakers on all sentence types in all tasks. Although aspect is certainly a difficult area to master, particularly because the meanings of the imperfect are acquired quite late, L2 learners are clearly able to overcome the parametric options of their native language. At least for this domain, it is suggested that access to Universal Grammar does not necessarily decay with age in L2 acquisition.