John Gill Commentary 2 Samuel 19:34

"And Barzillai said unto the king, How many are the days of the years of my life, that I should go up with the king unto Jerusalem?" — 2 Samuel 19:34 (ASV)

And Barzillai said to the king
In answer to the grateful proposal he made:

how long have I to live ;
that could not be said with exactness by any; but it might be probably conjectured from the age he was of, and the infirmities that attended him, that he could not live long; it was but a short time he had to be in the world:

that I should go up with the king to Jerusalem ?
take so long a journey as that, seeing he might die before he got there; and if he did not, since it could not be thought he should live long, he could not think of it, or judge it advisable at such an age to take such a journey, change his place of abode, and manner of living.