Bottom gating was used over a broad span of cast iron pan styles, mostly 1800s. You can tell more by looking at your pan and seeing what characteristics it doesn't have that an older pan that would have been bottom-gated would most likely have. On yours, the reinforcement ridge on the underside of the handle is blended in, not distinct. There is no triangular, rounded or lobed reinforcement pad at the base of the handle. Although not apparent in most of the photos, the top edge does not have a distinct reinforced rim. The handle is of the typical early to mid-20th century style, with the teardrop hanging hole, as opposed to the older "fancy" handle style.