1
general::
Phrase(s): There’s no fool like an old fool.
Prov. Cliché Old people are supposed to be wise, so if an old person behaves foolishly, it is worse than a young person behaving foolishly. • As old Mrs. Fleischman watched her husband try to dance the way their grandchildren danced, she muttered, "There’s no fool like an old fool."
McGrawhill's American Idioms And Phrasal Verbs
2
general::
An old fool is the worst kind of fool, as in He's marrying a woman fifty years his junior? there's no fool like an old fool. This adage, now considered somewhat offensive for stereotyping old people, appeared in John Heywood's 1546 proverb collection and has been repeated ever since., see NO FOOL LIKE AN OLD FOOL.
American Heritage Idioms