Isa 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; he who dies at a hundred will be thought a mere youth; he who fails to reach a hundred will be considered accursed.”
People who think that the 1000 year reign is figurative and not literal do have to try kind of hard to reconsile this prophesy.. I take it literal:
6 Blessed and holy are those who have part in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years.
I found this explanation online and I like after a bit of modification:
It is my understanding that this passage is referring to the state of affairs during the Millennium where Christ rules the earth for a thousand years after His Second Coming before turning it over to the Father. The church returns with Christ in their immortal, glorified bodies, at which time Christ resurrects the believers who have died during the Tribulation, along with the Old Testament saints (who are also granted immortality). This leaves the mortals who have physically survived the Tribulation period – unbelievers who resisted the mark of the beast – to face Christ’s judgment of the nations (Mat. 25:31-32). Those deemed to be goats (because they did not come to the aid of Christ’s “brethren” – in this context, the Jews) are executed, while the “sheep” (those who proved their faith by helping the Jews) enter Christ’s earthly kingdom in mortal bodies in order to repopulate the planet. We rule over them and teach them His ways.
Christ restores paradise conditions and the lifespan is restored to that of Adam’s day, so that as Isaiah says, if one dies at a hundred years of age, it would be considered as a child dying. During this thousand years, many will be born who will not accept Christ as their Saviour and will only feign obedience until Satan is released and gives them their opportunity to openly rebel (Rev. 20:7-10 ). Death and curse still remain because God has not yet made all things new. This won’t take place until after the Great White Throne judgment (see Rev. 20:7-15 and Rev. 21:1-4).
I see verse Isa. 65:18 indicating a change in thought (note the word “BUT”), where after declaring that God will create a new heaven and earth, He now changes the focus to Jerusalem during the Millennium. After the final judgment and the creation of the new heaven and earth, there will be no more curse, death or sorrow – just as John says.
I think the millenial reign will be like the garden of Eden, but Isa details the empire Jesus built as still having farming, technology and jobs. Which makes the ‘You will be ruler of 10 cities, 5 cities,’ prophesy really exciting.