H.M.S. Victory is the oldest commissioned warship (1765) but has been in dry dock as a museum ship since 1922.
U.S.S. Constitution is the oldest commissioned warship still in service (1797) but is no longer a warship but a sail-training ship.
Kommuna (formerly HIRMS Volkov under Imperial Russia and USSRS Kommuna under the Soviet Union) is the oldest commissioned warship still in active duty (1913)
According to Wikipedia she’s the oldest afloat but the Kommuna is the oldest in active service. Seems like semantics but I guess the Kommuna was actually being used as compared to being a museum ship.