It is military and was worn on the collar of a dress uniform. (Likely Army) but as far as an age, I'd say that it is older than WWII but I'll leave that up to those who know more. Cool find.
It is a US Army collar-disc insignia. The platform across its concave back held two brass "pins" (which are broken off of your insignia) for attaching this insignia to the Uniform collar's cloth. The platform in your insignia being made of brass dates your insignia to 1951-1970. For confirmation of that info, go to the following webpage and scroll down to "Post-World War Two Type V Collar Disks", and check the photos in that section: Dating Metallic Insignia: Collar Disks