'Old' in the Bible

Ish-bosheth, 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 that was lame of his feet. He was five years old when the tidings came of Saul and Jonathan out of Jezreel; and his nurse took him up, and fled: and it came to pass, as she made haste to flee, that he fell, and became lame. And 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 fourscore 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 fourscore years old: can I discern between good and bad? can thy servant taste what I eat or what I drink? can I hear any more the voice of singing men and singing women? wherefore then should thy servant be yet a burden unto my lord the king?

Then she spake, saying, They were wont to speak in old time, saying, They shall surely ask counsel at Abel: and so they ended the matter .