You didn't tell us whether it is a 1-piece button or 2-piece button, which is very imortant information for dating a button. See diagram below.
Also, we need to see well-focused closeup photos of its back, and a "sideview" photo.
Meanwhile... generally, a button saying gilt on its back dates from around 1790 through the 1870s. I said generally because there are a few later-dating exceptions. The era of your button will depend on whether it is a 1-piece or 2-piece button, and on whether the lettering on its back is "raised" letters or "indented" letters.