Hello fellow anon. For questions about the age of the earth and other evidences, try looking here for some answers http://apologeticspress.org/ as they do a good job of making a defense of things such as the age of the earth.
To answer your question about those who have never heard of God, read Romans 1:18 and following, but to summarize, neither the Jew nor the Gentile has an excuse for not knowing that there is a God, a Creator, and seeking him out. For the Jew it was because they had the Law of Moses, which as God says through Paul was a school master, a guide which leads us to Christ.
For those who are Gentiles/pagans, they are without excuse for the entire natural world shows the eternal, immortal qualities of God. But those who did not have the Law turned to creation and worshiped it, rather than the creator.
The truth is friend anon, the Christian faith is not something that is to be blindly believed, but it is a faith built on evidence after evidence.