Why does Maria Marez (Antonio's mother) say that "growing into manhood is a sin?"

Antonio’s mother believes that the passage into adulthood is dependent on an acceptance of sin. She believes that sin is the inevitable folly of man; loss of innocence and sin go hand in hand. The only way to grow up, she argues, is to be sinful and thus, only if Antonio becomes a priest will he be able to enter adulthood with his innocence.