Genesis 7:6
"And Noah was six hundred years old when the flood of waters was upon the earth."
Cross References (ranked by relevance)
Genesis 5:32
And Noah was five hundred years old: and Noah begat Shem, Ham, and Japheth.
Genesis 8:13
And it came to pass in the six hundredth and first year, in the first month, the first day of the month, the waters were dried up from off the earth: and Noah removed the covering of the ark, and looked, and, behold, the face of the ground was dry.