Is it possible that Jared and Methuselah would have been alive long enough to help Noah build part of the ark?
The only way to answer this question is to look at the genealogies that Genesis offers. But this is a tricky question because we do not know if there were any gaps in the genealogies presented in the book of Genesis.
I will take them to stand as they are and use them to mathematically decipher if it was possible for anyone to be alive during the time of Noah before the floods came upon the earth. The floods started when Noah was six hundred years old (Genesis 7:11).
We have to work backwards mathematically from the time of Noah through the genealogy to decipher how long people were living before the flood. The only way we have to do this is to go off of the moment that they became fathers to their firstborn sons.
For previous questions about the flood and the genealogies listed in Genesis, I created a chart based on the facts we have. Based on my calculations, Jared died the year of the flood. It is most likely this was when the flood came that he died. But the flood came in the same year that he died.
Methuselah would have still been alive. In fact, everyone except Enoch would have still been alive, including Jared, Methuselah, Lamech, and Noah. So it may have been that Noah had helped to build the Ark from his family and his family line.
Even though these people may still have been alive, none of them would’ve survived the flood. The Bible is very clear that of the eight people to go to the ark, these were not any of them.
We know that the neighbors of Noah were too busy making fun of him to help them build the ark. They do not believe that a flood would come because they had never seen one before. So it’s quite possible that he did not build it alone. At the very least, his sons would have helped him build it.