Genesis 7:6

“And Noah was six hundred years old when the flood of waters was upon the earth.”

KJV

Meaning

Noah is six hundred years old when the floodwaters begin, anchoring the event in the genealogy's chronology.

The age is a narrative datum; Genesis does not explain ancient longevity here or provide a biological mechanism for it.

The flood story is presented as part of the same ordered family chronology that has traced Noah's life to this point.