Always difficult to tell the age but most skeleton keys were popularly used in all homes prior to the 1940s. Could very well be over 100 years old - give or take 20 years. Someone told me this is likely for a chest and the number on the key would point to the type of chest but my research didn't reveal anything - 12W21 is imprinted on one side

Has a nice rustic look with surface rust only. Not bent or showing any other major flaws.