The present research tested the hypothesis that the age at which one's first language (L1) words are learned influences language processing in bilinguals. Prior research on bilingual language processing by Kroll and colleagues has suggested that memory links between L1 words and conceptual representations are stronger than memory links between one's second language (L2) word and conceptual representations. We hypothesized that the strengths of memory links between L1 words and conceptual representations are stronger for words learned early in life than for words learned later in life. Support for the hypothesis was obtained in bilingual translation experiment with 36 Spanish-English bilinguals. Participants translated L1 words into L2 and L2 words into L1. Half of the L1 words were learned early in childhood (early AoA words), and half were learned later in life (late AoA words). The L2 words were translation equivalents of the L1 words tested; the average age at which L2 words were learned was age 7. Target words were presented either in random order or blocked by semantic category. Translation times were longer when trials were blocked by semantic category (i.e., categorical interference) occurred only when early AoA L1 words were translated into L2. Implications for current models of bilingual memory are discussed.