Ok.
The best thing quoting an old source does is show the presence of a view or opinion that you want to establish as existing in the Tradition. The quote, by itself, has to have other factors than antiquity to give it weight.
It depends on the quote. Who made the quote. Under what circuмstance and authority? Was he authorized to teach in the name of the Church? Does he teach the common opinion of the moral majority of theologians on an issue? Was it something the Pope approved? Was it in an encyclical and put in the acta?
Was it a sainted Doctor of the Church?
For instance if two Sainted doctors of the Church along with all the theologians, and the Popes after the Council of Trent taught BOD. What are we to think? The question is rhetorical, but not for the feeneyites.