The following is a rough guide to Mouse Hole anvil age from Jim Wallace at the National Ornamental Metal Museum.
If the anvil does not have a step, has an even smaller horn than the small one on other Mouse Hole anvils, and is attached directly under the end of the face; then the anvil would have been made in the 1725-1775 time frame. It may or may not have a steel face.
If it has a step, and is made by Armatage, marked as an Armatage Mouse Hole, then the face is hard steel.
If there is no pritchell hole, it was made before about 1790-1795.
If it has a PUNCHED pritchell hole, it is in the 1795- 1850 manufacture range. Some of the older Mouse Hole anvils had pritchell holes drilled in them, to bring them up to a more "modern" configuration. The punched hardy and pritchell holes leave a slight bulge on the bottom, as they seem to have been through punched from the top, with no counter punching from below.
Some of the Mouse Holes had no horn. This indicates it is older, from the early 1725 period, but is not conclusive.