Bronze Age refers to a stage of development during which a society learns to cast bronze by smelting tin and copper and to use the alloy predominantly in tools, weapons, jewelry and cookware.
In the 24th century, the Mintakan civilization on Mintaka III was undergoing its Bronze Age, as they had not yet developed the techniques to forge iron. (TNG: "Who Watches The Watchers")
The Takarians of Takar were undergoing their Bronze Age when Dr. Arridor and Kol settled on their planet. (VOY: "False Profits")