The effects of age of acquisition (AoA) in the first (L1) and second (L2) languages of Spanish--English bilinguals were explored using a translation judgement task in which participants decided whether or not pairs of words in the two languages were translations of each other (i.e., had the same meaning). Experiment 1 found an effect of second language AoA on decision latencies which interacted significantly with first language AoA such that first language AoA only affected translation when the second language word in the pair was early acquired. It was hypothesised that slow processing of late acquired L2 words could have masked the AoA effect of the first language in Experiment 1. Analysis of lexical decision speeds in Experiment 2 lent support to this hypothesis. Experiment 2 also found lexical decision speeds in Spanish (L1) to be predicted by Spanish AoA and word frequency while lexical decision speeds in English (L2) were predicted by English (not Spanish) AoA, English word frequency and word length. In Experiment 3 main effects of both first and second language AoA were obtained when the L2 word in a pair was presented 400ms ahead of the L1 word. The results are discussed in terms of alternative accounts of how AoA may affect lexical processing and access to semantic representations.