The everlasting life that comes from having the son is getting to live forever without dying, remember that man was formed from dust and the only way to live forver in this condition is to have a supliment in this case the "Tree of life" which was in the garden of eden. Without eating from the tree man is bound to grow old and wax old like garment no matter what. That is why adam and eve did not die immidiately they sinned. The process of death begun from the time they ceased to eat from the "Tree of life"
Genesis 3: 22 (KJV) - And the LORD God said, Behold, the man is become as one of us, to know good and evil: and now, lest he put forth his hand, and take also of the tree of life, and eat, and live for ever:
Here we see that adam and eve would have continued to live forever after sinning if they had acces to the "Tree of life".
Until the time of Noah men could live for very long periods of time(800 years +) even though they evetually died, this trend stopped after the very sinful nature of the people in Noah's era caused God to flood the earth.
Now we see Jesus Christ who was(WORD- John 1:1) and still is(WORD INCANATE- John 1:14) the life which was in the "Tree of life".
So it comes down to when people are really going to eeat from the tree. From the scriptures we know that Christ is going to rule for a thousand years and there are going to be humans who would co-rule with him during this period of time, that is why Christ(being the life in the tree) would sustain them until that time is over.
Again in revelation,
Revelation 22: 2(KJV) - In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations.
We see that the Tree does not only sustain lives but it heals too, it makes whole from all infirmities cause by sin.