Indo-Pacific lionfish (Pterois volitans/miles) were first detected off the coast of Florida in the 1980s, with aquaria release being the most likely mechanism for introduction. Since then, lionfish have proliferated through the northwestern Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Here, we report the oldest lionfish aged on record in their invaded range, removed from Flower Garden Banks National Marine Sanctuary (FGBNMS). In August 2018, a research expedition removed 776 lionfish from FGBNMS, of which a subset were retained for age and growth estimation. The oldest lionfish aged was a 10 yr old male, with total length 375 mm and weight 805 g. The back-calculated birth date (2008) preceded the first observation of lionfish at FGBNMS by three years (2011). It is not well understood if lionfish are having negative impacts at FGBNMS, but this report signifies the importance of continued monitoring and removal efforts of this protected area.