Nature, it is often said, is God's "Second Book." It really should be considered the first, because all creation existed before the Bible was written. However, within the "book of nature," we have a big clue as to the answer for this question.
The DNA in every cell of our bodies must be replicated each time a cell divides, the daughter cell replacing the original cell. Except for meiosis, in which the haploid gametes are produced, the two DNA strands must be kept attached to each other to keep them correctly aligned. When cell division occurs, therefore, they are "unzipped" up to the maximum length that still keeps the two strands held together at the end, and the open portion is then copied. With each such copy, a part of the end of the DNA strand, called the telomere, grows shorter.
The telomeres are just extra lengths on the end of the DNA strand, containing no genetic information, and are there just for the purpose of allowing the actual genetic portions to be fully copied. But once the telomeres are shortened or lost to the point where the genes cannot be fully copied, genetic information that is important to cellular function is lost, and the cell soon dies (apoptosis). When enough of one's cells have reached this age-related threshhold, organ failure will eventually occur, and death is the result.
There is no elixir on earth that can lengthen those telomeres. Many creationist biologists believe that the Tree of Life is the key to doing this. In theory, by simply lengthening the telomeres periodically, one's life could be extended, potentially forever.
If this is related to the mechanism for prolonging one's life, it would indicate that the Tree of Life is something from which all of us would need to partake on a regular basis. Exactly how often that might be, we are not told. Obviously, daily consumption would be unnecessary. Would it be enough to eat the fruit of the Tree of Life once per year? Perhaps. The interesting detail that the Bible gives is that the Tree will yield twelve kinds of fruit per year--one per month.
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. (Revelation 22:2, KJV)
We also know that throughout eternity we will gather together at least once every week--on the Sabbath--so we would have at least weekly access to the Tree.
22 For as the new heavens and the new earth, which I will
make, shall remain before me, saith the LORD, so shall your seed and
your name remain. 23 And it shall come to pass, that from
one new moon to another, and from one sabbath to another, shall all
flesh come to worship before me, saith the LORD. (Isaiah 66:22-23,
The most important point is that in order to have the right to eat of the Tree of Life, one must keep God's commandments.
Blessed are they that do his commandments, that they may have right to
the tree of life, and may enter in through the gates into the city.
(Revelation 22:14, KJV)