I don't know if the flood was global or local. Either way I don't know when Noah was born so I don't know. There are gaps in other places in the bible regarding genealogies so there could be gaps in the biblical genealogies from the first human to Noah. Some believe those gaps are hundreds of thousands of years. In that case it wouldn't make much sense to list thousands of ancestors between the first human and Noah.
Well according to the original Sumerian version of the story in which a king called Atra-Hasis is warned by a god called 'Enki' about the other gods plans to kill humanity with a flood and instructs him to build a boat to save himself and his loved ones, it was a localised flood, apparently through a vally that contained all of humanity at the time. This version was later changed slightly in the version found in the Babylonian 'Epic of Gilgamesh' in which a commoner called Utnapishtim is given the same warning and boat building instructions by the same god and the flood is also changed to a global flood. This version also contains several things that are used in the final Biblical narrative. For example;
"The dove went out and returned" (Gilgamesh XI,147)
"sent forth the dove and the dove came back to him" (Genesis 8:10b-11)
"I sent forth a raven" (Gilgamesh XI,152)
"Noah... sent forth a raven" (Genesis 8:7)
"The gods smelled the sweet savor" (Gilgamesh XI,160)
"And the Lord smelled the sweet savor..." (Genesis 8:21)
"On Mount Nisir the boat grounded" (Gilgamesh XI,140)
"the ark came to rest upon the mountains" (Genesis 8:4)
"The cattle of the field, the beast of the plain" (Gilgamesh XI,85)
"clean animals and of animals that are not clean" (Genesis 7:8)
"into the ship all my family and relatives" (Gilgamesh XI,84)
"Go into the ark, you and all your household" (Genesis 7:1)
"pitch I poured into the inside" (Gilgamesh XI,66)
"cover it inside and out with pitch" (Genesis 6:14)
"And offered a sacrifice" (Gilgamesh XI,155)
"offered burnt offerings on the altar" (Genesis 8:20)
"he touched our foreheads to bless us" (Gilgamesh XI,192)
"And God blessed Noah" (Genesis 9:1)
So the Biblical account is pretty obviously based upon the earlier Gilgamesh version then, (which in turn is based upon the much earlier Sumerian version) infact if all of the authors were still alive, the author of Gilgamesh would have no problem suing the author of the Genesis version for plagiarism.
But this raises an interesting point, I take it from your posts (and please forgive me if I'm wrong about this) that you are a Christian? If that's the case then you must obviously consider the Sumerian gods to be mythological, true? So if the flood story in the Bible is based upon mythology, then doesn't that make the Biblical story itself mythological? After all, you cannot base truth upon mythology. You can base mythology upon truth, but not the other way around.