Middle English manhede, manhode, "state of being human" (early 13c.), from man (n.) + -hood. Sense of "manliness, qualities considered becoming to a man" (variously: "courageous behavior, bravery; courteous behavior, gentility; compassion, kindness") is from c. 1300. Meaning "state of being an adult male" is from late 14c.
Similar words in Old English also were less explicitly masculine: manscipe "humanity, courtesy," literally "man-ship;" mennisclicnes "state of man, humanity, humaneness, human nature" (compare mannish). The more purely "manly" word was werhad "male sex, virility, manhood" (see first element in werewolf).