'Old' in the Bible

Ishbosheth, Saul's son, was forty years old when he began to reign over Israel, and he reigned two years. But the house of Judah followed David.

Now Jonathan, Saul's son, had a son who was lame of his feet. He was five years old when the news came of Saul and Jonathan out of Jezreel; and his nurse took him up, and fled: and it happened, as she made haste to flee, that he fell, and became lame. His name was Mephibosheth.

David was thirty years old when he began to reign, and he reigned forty years.

Now Barzillai was a very aged man, even eighty years old: and he had provided the king with sustenance while he lay at Mahanaim; for he was a very great man.

I am this day eighty years old. Can I discern between good and bad? Can your servant taste what I eat or what I drink? Can I hear any more the voice of singing men and singing women? Why then should your servant be yet a burden to my lord the king?

Then she spoke, saying, "They were used to say in old times, 'They shall surely ask counsel at Abel;' and so they settled it.