Why do Christians believe in that stupid the earth is 4,000 to 6000 years old?

I’m down which Christian as far as morals and way of life they thing “God’s time isn’t or time” right hence why im agnostic I can’t believe the earth is 4000-6000 years old why do Christians believe this

Why do Christians believe in that stupid the earth is 4,000 to 6000 years old?
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