ONE DAY IS AS A THOUSAND YEARS WITH THE LORD

And the Lord God commanded the man, saying, Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die. (Genesis 2:16, 17 KJV)

But, beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day. (2 Peter 3:8 KJV)

Because a day is like a thousand years before the Lord, and the Lord had commanded that in that day you eat of the fruit, you will die, no one lived, is living or will ever live past a thousand years. Methuselah was the oldest person that ever lived and he lived for 969 year and he died.

We can apply this principle of a day with the Lord is a thousand years to understand that the world was made in 6000 years. 

And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day. (Genesis 1:31 KJV)