I don't work out what does idiom mean

[golf]

Test No. incompl/inter-14 "Popular Idioms (1)", question 6

There's no fool like an ......... fool.

(a) aged
(b) ancient
(c) elderly
(d) old

Test No. incompl/inter-14 "Popular Idioms (1)", answer 6

There's no fool like an old fool.

Correct answer: (d) old

Hi Alan, Can you help me I didn't work out what these idiom mean...
Thank you for your kindness

I love your website so much now i'm a english-test.net addict now ... hehehe will come back to get answer from you

[Alan]

Hi,

It suggests that if you do something stupid/foolish, it's worse if you are old because when you are older, you should be wiser.

Alan
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