ANSWER: The question was, How old is the earth according to catholics. In fact, the Catholic Church takes no position on the age of the earth, and, like most Christian churches, it has no problem with evolution. Anyone attempting to score points attempting to present inaccurate information in that regard does science no favours.
Roman Catholic Answer
The Catholic Church has no official position on the age of the earth. The Catholic Church is the Mystical Body of Christ on earth, commissioned to go out to all the nations, baptizing them, and preaching the Word of God (Jesus). The Catholic Church is not concerned with government, physical sciences, etc.
per se, but is concerned with getting people to heaven. The Bible addresses the creation of the world, and Catholics are obliged to believe that God created the world out of nothing. How, or when, He did that is neither addressed, nor important to our eternal salvation.
As it explains in the Catechism of the Catholic Church, "The inspired books teach the truth. 'Since therefore all that the inspired authors or sacred writers affirm should be regarded as affirmed by the Holy Spirit, we must acknowledge that the books of Scripture firmly, faithfully, and without error teach that truth which God, for the sake of our salvation, wished to see confided to the Sacred Scriptures.'"
... To interpret Scripture correctly, the reader must be attentive to what the human authors truly wanted to affirm and to what God wanted to reveal to us by their words."
...the reader must take into account the conditions of their time and culture, the literary genres in use at that time, and the modes of feeling, speaking, and marrating then current."
-> In other words, take the first couple chapters of Genesis. God created the whole world, and everything in it out of nothing. To try and read it as a modern scientific text is a mistake, and misses the point that God is trying to make. An example of this mistaken approach would be the first answer above.
The earth is as old as it is, in God's good time, and we don't have to worry about it. We have to worry about what Jesus told us to do.