In ancient Rome and Greece, large penises were seen as comical or grotesque, not sexy. They were really into pederasty back then, so for them, the ideal penis was small and thin with a foreskin--a boy's penis.
Also, note that Michelangelo's women don't look very feminine. That's because female nudes were out of the question back then; lacking any references, and having access only to male models, he simply painted men, stuck breasts on them, and left off the dicks. He really had no idea what a female body actually looked like. He tended to paint babies using the same method--as scaled-down, chubby adults. That's why his women look masculine (see the Sistine Chapel) and his baby-angels look surprisingly buff.