John Gill Commentary 2 Samuel 19:32

"Now Barzillai was a very aged man, even fourscore years old: and he had provided the king with sustenance while he lay at Mahanaim; for he was a very great man." — 2 Samuel 19:32 (ASV)

Now Barzillai was a very aged man, [even] fourscore years old ,
&c.] Which was ten years beyond the common term of man's life, and reckoned a very great age in David's time, and has been ever since, and still is, see (Psalms 90:10);

and he had provided the king of sustenance while he lay at Mahanaim :
had supported him and his family, furnished him with provisions, and all the necessaries of life, during his stay there:

for he [was] a very great man ;
in wealth and riches, and was a very liberal man, and a man of great wisdom and good sense; and very probably was a man of great grace, which taught him his duty to his prince, and influenced him to show mercy to him in distress.