Is this an ambrotype for sure? I know the image quality is better than most tintypes, but it could still be one. Early examples were reverse images as well and could be hand tinted. If it’s a tintype, there might be some sort of insignia or impression in the edge of the photo that could help further date it. If it’s an ambrotype, you can sometimes make a further guess on the date when looking at any case or frame it was in. Both types of photos were developed around the same time in the mid 1850s, but tintypes are said to have become popular around 1860 by which time ambrotypes had already been popular for a few years.
I’ve read that large cravats tied horizontally like the man in the photo’s were popular from the 1850s to the mid 1860s. They became progressively larger within that time frame until the mid-1860s when they were replaced completely by slimmer and more refined neckties.
Any which way, I would say this probably dates between 1855-1865.