'Old' in the Bible

Ish-bosheth, Saul’s son, was forty years old when he became king over Israel, and he reigned for two years. But the house of Judah followed David.

Jonathan, Saul’s son, had a son whose feet were crippled. He was five years old when the news [of the deaths] of Saul and Jonathan came from Jezreel. And the boy’s nurse picked him up and fled; but it happened that while she was hurrying to flee, he fell and became lame. His name was Mephibosheth.

David was thirty years old when he became king, and he reigned forty years.

Now Tamar was wearing a [long-sleeved] robe of various colors; for that is how the virgin daughters of the king dressed themselves in robes. Then Amnon’s personal servant took her out and bolted the door behind her.

Barzillai was a very old man, eighty years old; and he had provided the king with food while he stayed at Mahanaim, for he was a very great and wealthy man.

I am this day eighty years old. Can I [be useful to advise you to] discern between good and bad? Can your servant taste what I eat or drink? Can I still hear the voices of singing men and women? Why then should your servant be an added burden to my lord the king?