In reading Isaiah 65:20 “”Never again will there be in it an infant who lives but a few days, or an old man who does not live out his years; the one who dies at a hundred will be thought a mere child; the one who fails to reach a hundred will be considered accursed.” NIV – I got to thinking, can you still die when we reach New Creation? (aka Heaven)

https://www.epm.org/resources/2010/Mar/28/isaiah-6517-it-sounds-if-isaiah-saying-new-heavens/ – this site leads to some interesting introspection on the subject. 

http://www.prca.org/resources/publications/cr-news/item/1384-is-there-death-in-heaven-1 – This site is more firm on the fact that this is not possible. They state the following verses for clarity: “The reader also refers to Revelation 21 and II Peter 3 as proof that death shall not enter the new creation. Revelation 21:4 declares, “And God shall wipe away all tears from their eyes; and there shall be no more death …” II Peter 3:13 is probably the verse to which the reader refers: “Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness.” Surely, where righteousness is, death cannot be, for death is the punishment for sin.”

It appears to me that Isaiah seems to be using the term of someone dying at 100 to be very young, as a way of saying it is unfathomable because people live for eternity and that is how he was trying to explain such a long process.