I read your post and subsequently, my pastor mentioned about Methuselah. I came back and tried to study the meaning of his name.
Methuselah comes from muth, a root that means "death"; and from shalach, which means to bring, or to send forth. The name Methuselah means, "his death shall bring".
The Hitchcock's Bible Name Dictionary says Methuselah means "he has sent his death".
Well, at least we know that his name means that "when he dies, it will come" (as defined by my pastor).
Interestingly, another web-site interprets Shalah as:
Shalah: the word for 'current' as is a river. In Hebrew their are fields of Shalah meaning irrigated fields and fields of Baal meaning watered by the god of thunderstorms - rain. Rivers in the ancient world represented decision or judgment, Shalah corresponds to the river Hubur in Mesopotamian mythology which one crossed to go to the underworld.
Whichever interpretation to take, of Shalach, or Shalah, Methuselah's name was a prophecy. As mentioned by my pastor, and as I've read in another bible study, "Methuselah's father was given a prophecy of the coming Great Flood, and was apparently told that as long as his son was alive, the judgment of the flood would be withheld; but as soon as he died, the flood would be brought or sent forth."
His name was constructed, Methuselah .. "when he dies, it will come" with insinuations of death, flood, judgement.
Why was Methuselah the longest person to live in the history of this world? I believe that God delayed the judgement of the people and therefore had to prolong Methuselah's life. God said that there will no longer be a great flood to wipe all of us off, but there is a coming Judgement Day. I also believe that God is also delaying this because in His heart, He wants everybody to be saved ...
There was a prophecy by pastor Dinakharan. He saw God convening with others in heaven and the people were urging Him to expedite judgement because the sins of the world was rising up to heaven, but God's response was "What about my desire that none should perish?".
Methuselah's long age is a sign of God's love and mercy for the people. He prolonged Methuselah's life to delay judgement. Hopefully, with the delay of the second judgement more of us will choose eternal life.
This is the site that talked about Methuselah: