It is not speculation. Just look at the release date for AoE 1 DE and AoE 2 DE, then compare how long each game had their Beta period, before the game was released.
AoE 3 DE Beta started in February. Then the release will definitely not be more than 1 year away. However, it is not likely that the come will release exactly in february (as was the case for AoE 1 DE), since the devlopers/publishers will want to capitalaize on the current “plague of death” (this is a euphemism), going around the world.
Therefore, the time window for the release of the game, would be around July-October of this year. Although they could aim for a December release for the holidays, however it would be more profitable to avoid competition by not releasing the game any later than november.
Also, do note, that since the Beta started in February of this year, it is extremely likely that the Beta for the game, will not have such a prolonged continuation for such a duration, as to be longer than 1 year. Since the game would lose the “potential maximum hype”, causing some consumer to lose interest, which would cause a possible decline in overall sales (at least in the short term), and would thus not be economical from a management or business venture, perspective.