You know I never understood that. I know in my heart God created the heavens and the earth, but I just never understood the necessity of trying to stick it within 6,000 years.
Me neither.
The idea that creation was 6,000 years ago comes from Bishop James Ussher of the Church of Ireland. In 1650 he added up the ages of the patriarchs in the "begats" and published a book called "Annals of the Old Testament" in which he stated that the earth was created at midday on 23 October 4004 BC.
Now, those who claim the earth was created about 6,000 years ago (4,004 + 2,006 = 6,010) apparently don't know where that idea came from.