Following are highlights from Genesis 5:28 - 9:29 from the World English Bible (WEB) translation for the purpose of clarifying how long the flood was and its relation to Noah's life.
Genesis 5:28-29 Lamech... became the father of a son. He named him Noah, saying, “This one will comfort us in our work and in the toil of our hands, caused by the ground which Yahweh has cursed.”
Genesis 5:32 Noah was five hundred years old, then Noah became the father of Shem, Ham, and Japheth.
Genesis 6:3 Yahweh said, “My Spirit will not strive with man forever, because he also is flesh; so his days will be one hundred twenty years.”
Genesis 6:18 I will establish my covenant with you. You shall come into the ship, you, your sons, your wife, and your sons’ wives with you.
Genesis 7:11-12 In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on that day all the fountains of the great deep burst open, and the sky’s windows opened. It rained on the earth forty days and forty nights.
Genesis 7:24 The waters flooded the earth one hundred fifty days.
Genesis 8:3-7 The waters continually receded from the earth. After the end of one hundred fifty days the waters receded. The ship rested in the seventh month, on the seventeenth day of the month, on Ararat’s mountains. The waters receded continually until the tenth month. In the tenth month, on the first day of the month, the tops of the mountains were visible. At the end of forty days, Noah opened the window of the ship which he had made, and he sent out a raven. It went back and forth, until the waters were dried up from the earth.
Genesis 5:28-29 Lamech... became the father of a son. He named him Noah, saying, “This one will comfort us in our work and in the toil of our hands, caused by the ground which Yahweh has cursed.”
Genesis 5:32 Noah was five hundred years old, then Noah became the father of Shem, Ham, and Japheth.
Genesis 6:3 Yahweh said, “My Spirit will not strive with man forever, because he also is flesh; so his days will be one hundred twenty years.”
Genesis 6:18 I will establish my covenant with you. You shall come into the ship, you, your sons, your wife, and your sons’ wives with you.
Genesis 7:11-12 In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on that day all the fountains of the great deep burst open, and the sky’s windows opened. It rained on the earth forty days and forty nights.
If we interpret 5:32 to mean Noah began having children at the age of 500, and 7:11 says the flood came when he was 600 years old, that means the ark took just shy of a century to construct and otherwise prepare for the flood. Further, we could estimate that it took perhaps 25 years from when he had his first son to when his youngest son got married, which only leaves about 75 years for the ark (considerably less than a century). Back in 6:3, if God had spoken that 120 years bit to Noah, it might be more compelling to believe it related to the ark, but it's just a random comment in the midst of 6:1-12, which was more generic backstory to what began when God first spoke to Noah in 6:13.Genesis 7:17 The flood was forty days on the earth. The waters increased, and lifted up the ship, and it was lifted up above the earth.
Genesis 7:24 The waters flooded the earth one hundred fifty days.
Genesis 8:3-7 The waters continually receded from the earth. After the end of one hundred fifty days the waters receded. The ship rested in the seventh month, on the seventeenth day of the month, on Ararat’s mountains. The waters receded continually until the tenth month. In the tenth month, on the first day of the month, the tops of the mountains were visible. At the end of forty days, Noah opened the window of the ship which he had made, and he sent out a raven. It went back and forth, until the waters were dried up from the earth.
Notice in 7:11, the "fountains of the great deep burst open" "on the 17th day of the second month" [of the year]. In 7:12 and 7:17 it says it rained for 40 days and nights. In 7:24 and 8:3 the flooding was claimed to last 150 days. If an average month lasted 30 days, that's exactly 5 months. In 8:4 the ark landed on the 17th day of the seventh month, which is again exactly 5 months to the day from when the great deep burst open. The alignment of all these numbers is reason to think someone cared about (bothered to) accurately recording a real event.Genesis 8:10-14 He waited yet another seven days; and again he sent the dove out of the ship. The dove came back to him at evening and, behold, in her mouth was a freshly plucked olive leaf. So Noah knew that the waters were abated from the earth. He waited yet another seven days, and sent out the dove; and she didn’t return to him any more. In the six hundred first year, in the first month, the first day of the month, the waters were dried up from the earth. Noah removed the covering of the ship, and looked. He saw that the surface of the ground was dry. In the second month, on the twenty-seventh day of the month, the earth was dry.
In 7:11 the "fountains of the great deep burst open" when Noah was 600 years, 2 months, 17 days old. In 8:12 the waters were all dried up when Noah was 601 years, 1 month, 1 day old. With a typical 30 day month and 12 months in a year, that makes a duration from flood to effective dryness 10 months and 13 days (or 313 days). Or between 7:11 and 8:14, the duration from begin to the very end was 1 year and 10 days.Genesis 9:28-29 Noah lived three hundred fifty years after the flood. All the days of Noah were nine hundred fifty years, and then he died.