Answer:
Because of the exponential advancements in technology.
Explanation:
The reason why the person who will live to be over 300 years of age is going to be only 10-20 years younger than the person who will live to be 200 years old is because of the exponential advancement rate in technology. It will come to a point where it will only take us 10-20 years of research and development to extend the human life from 200 to 300 years.
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