Coinshooter, sorry I cannot give you any info on that button... But it is a great find, and in very nice condition.... Which is great in any collection, old or not.....
This appears to be a post-WWII civilian dress or blazer button made in imitation of a U.S. Navy uniform button pattern which was used from about 1850 until 1941. On the original Navy buttons (see example below) the eagle & anchor were surrounded by stars and a rope border— features missing on yours, although some imitations include those as well.
I know almost nothing about buttons and would believe anything PBK tells me... that button looks older though, again, I don't doubt he's right, just .. wow. If I dug that I would've done the happy dance thinking I had an old one.
Nice button! I found one that looks a lot like this last year. Here is the link to the picture I posted. Mine turned out to be more modern than I thought. Good Luck!