The present study examines the production outcomes of late second language (L2) learners in order to determine if the mechanisms that allow the creation of phonetic categories remains available during the lifespan, as the Speech Language Model (SLM) claims. In addition, the study focuses on the type of interaction that exists between the first language (L1) and L2 phonological subsystems. Given the participants' proficiency level, L1 influence on the L2 is expected, while a bidirectional L1-L2 interaction is unlikely. The main tool used to examine language interaction and category development is VOT (voice onset time) production in monolingual and code-switched (CS) sentences. Participants, then, serve as their own control against which production in CS sentences is compared. The results confirm the availability of L2 phonetic category formation for late L2 learners, while different patterns of L1-L2 uni- and bidirectional interaction indicate that different places of articulation may pose various levels of difficulty in terms of ease and pace of acquisition. (Contains 3 tables, 4 figures, and 7 notes.)