Age of arrival (AOA) has been shown to predict successful L2 phonological acquisition among transnational bilinguals: the earlier acquisition begins, the more native-like the L2 phonology. AOA studies have been submitted as evidence for the Critical Period Hypothesis. However, recent research explains the AOA effect through other sociolinguistic factors that may be correlated, such as quality of L2 input. This study examines a population of Korean-English bilinguals, grouped by AOA and generational status. It is hypothesized that the earlier the AOA, the more likely a speaker is to participate in back vowel fronting, part of the California Vowel Shift. Natural speech data taken from bilingual interviews shows that AOA has, in fact, no effect on back vowel fronting, although gender does. Second generation Korean Americans (L1 English) and early childhood immigrant Korean Americans (L2 English) behave almost the same with respect to this sound change of California English.