Though Paul is making a generalization of all humanity, we would agree that there are exceptions. For example, a child below the age of reason is not capable of committing actual sin. By definition he can’t sin, since sinning requires the ability to reason and the ability to intend to sin. This is indicated by Paul later in the epistle to the Romans when he speaks of the time when Jacob and Esau were unborn babies as a time when they "had done nothing either good or bad" (Rom. 9:11).
Jesus is another significant exception to the rule, having been exempt from actual and original sin (Heb. 4:15). If Paul’s statement in Romans 3 includes an exception for the new Adam (Jesus), one may argue that an exception for the new Eve (Mary) can also be made.
It is written in Holy Scripture according to Luke:
28 And the angel being come in, said unto her: Hail, full of grace, the Lord is with thee: blessed art thou among women.
41 And it came to pass, that when Elizabeth heard the salutation of Mary, the infant leaped in her womb. And Elizabeth was filled with the Holy Ghost: 42 And she cried out with a loud voice, and said: Blessed art thou among women, and blessed is the fruit of thy womb. 43 And whence is this to me, that the mother of my Lord should come to me? 44 For behold as soon as the voice of thy salutation sounded in my ears, the infant in my womb leaped for joy. 45 And blessed art thou that hast believed, because those things shall be accomplished that were spoken to thee by the Lord.
46 And Mary said: My soul doth magnify the Lord. 47 And my spirit hath rejoiced in God my Saviour. 48 Because he hath regarded the humility of his handmaid; for behold from henceforth all generations shall call me blessed. 49 Because he that is mighty, hath done great things to me; and holy is his name. 50 And his mercy is from generation unto generations, to them that fear him.
When is the last time that you called the Mother of Our Savior Blessed?
Our Blessed Mother always points us, her children to Our Lord.