HMS Amazon was technically possible earlier

How much earlier could the Royal Navy have built HMS Amazon?

Technically well before the 1920s, since its principal machinery already existed before World War I.

Brown-Curtis geared turbines and three-drum Yarrow boilers were available before the First World War. A similar large destroyer could therefore have been built earlier if the Admiralty had wanted and funded it. The limiting factor was need rather than machinery: Britain entered the interwar period with dozens of V/W- and S-class destroyers already available. Amazon and Ambuscade became attractive when the Royal Navy required a modern successor and experimental route toward the later letter classes, not when a new enabling technology suddenly appeared.