A set phrase meaning that something is not new or surprising; it has been that way all along. Often used to dismiss a complaint or observation as nothing out of the ordinary.
His being late is nothing new.
It's the same old story—another price hike.
From 今に (now) + 始めぬ (archaic negative of 始める, 'to begin'), literally 'it does not begin now.' The negative form ぬ is classical, giving the phrase a slightly literary or proverbial feel.