@r_speir is clearly an OEC, not a YEC, regardless of what he says.
The proper way of interpreting a text is to understand what the original author meant by it and how the original audience understood it. Using legal terminology, this is not “textualism” but “originalism”. In hermeneutics it’s called “grammatical-historical”, which I know you understand. That’s a sort of combination of “textualism” and “originalism” which claims that the text has one objective meaning which can be determined from what the text meant in its proper historical context.
It is totally impossible to believe the original audience understood things like the “gap theory” or the “day age” theory. The only way one can justify those types of interpretations is by making religious assumptions about the nature of the text. You have to assume that God spoke things to Moses or whomever that he did not understand or communicate clearly, and that the text contains true things from God which Moses (or whomever) simply missed or misinterpreted. This would mean that God either failed to communicate His meaning or was intentionally hiding things from Moses et al. One is free to believe that, but that belief does not come from the text or the grammatical historical method. It comes from the need to harmonize the text with modern science and includes additional assumptions about God’s purpose which are nowhere evident. The “grammatical historical” interpretation requires no such assumptions about either God or modern science. In fact, one doesn’t even have to believe in God at all to use it.