Among papers considering L2 performance, a subset take into account the length of residence (LOR) in the country where the L2 is spoken. In about half of these, LOR makes no difference for performance of at least one variable measured. Since those who reside in an L2 environment for many years tend to be older, the beneficial effects of longer LOR may at some point be counteracted by declines due to aging. This article draws on research in cognitive aging to consider how age could impact L2 performance. This is particularly important when investigating the effects of LOR or age of L2 acquisition since LOR, age of acquisition, and age at testing are linearly dependent variables, making conclusions based on any of these variables problematic. We argue that aging is a largely ignored confound in the literature on L2 attainment, particularly for studies that include older adults in their samples.