Question: How long will Old Paul live for?
Answer: Paul and the mouse both aged considerably. No one ever said they weren't aging, just that the power from John was making them live extremely long lives.
Answer: If Paul could live to be that old then he would still be looking young. He would not be looking like a centenarian.
Gravity is relentless.
Answer: Since John Coffey was able to die via execution, we can assume that Paul could be killed. This means that, like John, Paul would have to choose to die. All we know is that John gave Paul a piece of himself - perhaps that piece was immortality?
Answer: At the end of the movie, it's discovered that Mr. Jingles is 64 years old. This is about sixteen times the life span of a regular mouse. Since this logic could apply to Paul, he could live anywhere between 1,300 and 1,500 years.
Nice idea but the math ain't mathin'. Your equation presumes that Mr. Jingles dies at age 64. But he is still alive! It seems more likely that John Coffey gave Paul and Mr. Jingles an indefinite natural life. They live forever unless something kills them. I'm sure if Paul was in a plane explosion over the Atlantic, he would die.
This is actually much simpler than either one of you are making it out to be: the answer is, there is no answer. We know that Paul and Mr Jingles are going to live longer lives because of John Coffey, and anything beyond that is pure speculation. I think this was intentionally left vague to keep the audience without a clear answer to Paul's fate, just like Paul is left without a clear answer.
jshy7979
It is implied in one of the very last shots that Mr. Jingles dies. Furthermore, Paul specifically says in the voice-over that he will not have an indefinite life, just an extended life.