[zeugma]

I think one can still be a Christian without believing God literally made the Earth 6000 years ago. In fact, there is a lot of debate even among Christians who interpret Scripture literally or figuratively.

I have never seen any claim in my bible that the earth was made 6000 years ago.

[Alas Babylon!]

Totally agree, but some people, in the past and even today, have gone through extraordinary mental gymnastics to say it is so.

Probably the greatest example is James Ussher, Bishop in the Church of Ireland, from 1625 to 1656, who calculated all the ages of Jesus's human ancestry, all the begats, and "Proved" that since Adam, the age of the Earth.

So subsequently, a large amount of Christians in diverse places have believed it is biblically-based.

The debate is explained well here.