The question “how old was Noah when he built the ark?” is one of those classic Bible trivia questions, right up there with “how old was Methuselah?” While it would be easy to give the basic answer, there’s a lot of background material that’s worth knowing. Knowing not just how old Noah was when he built the ark, but whether living that long was unusual for his generation, gives us a snapshot of what life was like before and after the flood.

How old was Noah when he built the ark?

Occasionally, people will say it took Noah 120 years to build the ark. However, this seems to be a misunderstanding based on a number given in Genesis 6:3. According to Genesis 7:6, Noah was 600 years old when the flood happened. However, the Bible doesn’t clarify how old Noah was when God commissioned them to build the ark. It mentions that God became sick of humanity’s wickedness in Genesis 6:5-8 after Noah had his sons. Assuming these events are in chronological order, that means God decided to wipe out humanity at some point after Noah was 500 years old.

We do get one telling detail in the story of God commissioning Noah. After God tells Noah that he’s going to wipe out most of humanity and gives Noah the details for making the ark, God tells Noah, once the boat is finished, to “enter the boat—you and your wife and your sons and their wives,” detailed in Genesis 6:18. Therefore, Noah must have not only had sons at this point, but those sons must also have been married by this point.

We don’t know whether Japheth and Ham started having kids before or after the flood, which might give an idea of how long his sons had been married when the flood happened. Given that Ancient Near Eastern cultures seemed to marry young, and men could father children well past 100 in this period, Noah’s sons could have been anything from teenagers to their 90s when the ark-building project began. Many scholars guess that Noah’s sons were in their 20s when they married, which would make Noah at least 520 years old when he started building the ark.

How old was Noah when the flood came?

According to Genesis 7:6, “Noah was six hundred years old when the floodwaters came on the earth.” This is reiterated in verse 11. The flood lasted about a year, and in Genesis 8:13, we find that “by the first day of the first month of Noah’s six hundred and first year, the water had dried up from the earth.” Genesis 9:28–29 sums it up: “Noah lived 350 years after the flood. Noah lived a total of 950 years, and then he died.”

Noah is the last of the long-lived patriarchs of old. Genesis 5 lists men who lived incredibly long lives, most of them over 900 years. After the flood, the ages to which people lived began to drop precipitously. Genesis 11 gives another list of men after the flood, and, by the time of Abraham, the average was around 200 years, which is still incredibly long by today’s standards. Abraham lived to be 175, according to Genesis 25:7.

How old was Noah when he died?

Genesis 5-10 gives a timeline of Noah’s family, which allows us to see how old Noah was when he died and how old he was at crucial moments in his life. According to Genesis 5:28-30, Noah was born to Lamech, son of Methuselah and grandson of Enoch. Lamech was 182 years old when he had Noah, and the name relates to a Hebrew word for “relief,” as seen in Genesis 5:29. Lamech died at 777 years old, making Noah 595 years old.

When Noah was 500 years old, he had his first of three sons: Shem, Ham, and Japheth. Ham was the youngest, and while translations vary, Genesis 10:21 seems to indicate that Japheth was the older brother of Shem. The critical factor is that Shem was 98 old when the flood happened and 100 when he had his first son, described in Genesis 11:11, which means Noah would have to be 502 when Shem was born. Therefore, Japheth was the oldest son, with Shem being born two years later.

Noah lived for 350 years after the flood and died at 950 years old. This means he lived long enough to not only see the land restored after the flood but to see all three of his sons start their families and multiply. His son Shem started the family line that led to Abraham, where we get the term “Semite,” or descendants of Shem.

Why did everyone have a shorter lifespan after the time of Noah?

Genesis 5 gives the genealogy of Adam through his son Seth, all the way to Noah. The next chapter starts with “then the people began to multiply…” and that God’s response was “My Spirit will not put up with humans for such a long time, for they are only mortal flesh. In the future, their normal lifespan will be no more than 120 years,” as seen in Genesis 6:2. So, sometime in Noah’s generation or in his sons’ generation, God decided that 120 years was the maximum lifespan that people could have.

Of course, a variety of Israelite patriarchs lived longer than this. Abraham lived to be 175 years old, and his son Isaac lived to be 180 years old. Moses lived to be 120 years old, “yet his eyesight was clear, and he was as strong as ever,” according to Deuteronomy 34:7. The fact that the Bible felt the need to highlight how healthy Moses was when he died could mean that by his time, it was rare to live that long and that well. No such comments are made about Abraham or Isaac. We know that Isaac had terrible eyesight in old age. His son Jacob famously used that to fool him in Genesis 27. So, at least in Moses’ case, this could be God giving long life and excellent health to someone, so he could complete the tasks that God had planned for him.

However, these examples of old age could also mean that the 120-year limit didn’t start immediately. There may have been a gradual genetic breakdown, with each generation living a shorter lifespan. Some biblical scholars have argued that the first few generations of humans must have had perfect genetics because Genesis mentions a certain amount of inbreeding without it resulting in problems. Adam’s three sons presumably married their sisters. Abraham married his half-sister Sarah, yet their son Jacob isn’t described as having the genetic issues that inbred children have today. If God made humans with perfect genetics and then, like the rest of creation after the fall, something in humanity was broken and tainted. It’s possible it took a few generations for the changes to become noticeable.

Noah is a man that endured a lot in a short time. Swallowing the fact that God was going to wipe out most of humanity would be challenging in itself, much less hearing that his family had been selected as the ones who would start things over. Then he had to figure out how to build the ark, trusting that God was with him the whole time and this massive project would work out.

As hard as it would be to build an ark, being inside it with all the animals and no idea when they could get out, would have been incredibly difficult. Noah and his family were inside the ark for about a year, according to Genesis 8:13-14. Yet there are no records of Noah giving up on trusting God during that time. He stayed faithful in this challenging time.