'Old' in the Bible

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

Now Jonathan, Saul’s son, had a son crippled in his feet. He was five years old when the report of Saul and Jonathan came from Jezreel, and his nurse took him up and fled. And it happened that in her hurry to flee, he fell and became lame. And his name was Mephibosheth.

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

Now Barzillai was very old, being eighty years old; and he had sustained the king while he stayed at Mahanaim, for he was a very great man.

I am now eighty years old. Can I distinguish between good and bad? Or can your servant taste what I eat or what I drink? Or can I hear anymore the voice of singing men and women? Why then should your servant be an added burden to my lord the king?