Literalists vary in their estimate of the Earth’s age, mostly by how literally they interpret a seven-days creation. Ussher’s calculation for the age of the Earth was actually 4004 BC, but I wholeheartedly agree that the age of the Earth actually is irrelevant to faith. Those who object to that regard the need to accept the dating as relevant because they believe anything they hold to be non-literal undermines the veracity of the entire Bible.
How anyone with a modern brain could possibly think that Bishop Ussher was right boggles the mind. He gave a date of December something, 4004 bc based on his calculation of the number of years in the begats. Since a careful reading of the bible indicates that these were listed as years, not months and days, then it is impossible to come up with a precise date. Rather it is an indication of the need to present the faithful with a date certain in a prescientific culture.