Five to Twelve — Edmund Cooper

The twenty-first century is drawing to an end. Earth's social structure has undergone a complete reversal - women dominate society and men have been reduced to the status of manipulated objects.
Into this world comes Dion Quern, a self-styled troubadour who refuses to conform to the social norm. But he discovers that women are superior to men in both bodily strength and number. And how can one man hope to change a whole society?