Learn English – Idiom or proverb request for describing or criticising a situation in which the lowliest dare mock a mightiest who has become old

I am looking for an idiom or proverb that can be used in situations which the lowliest dare mock a mightiest because of his/her age and thus considering him/her enfeebled.

There is proverb in Persian which literally means:

"The jackal derides an old lion".

The connotation or implication of the proverb is that age destroys even the mightiest (= the lion) and most noble, to the extent that the lowliest (= the jackal), who would have never dared in his prime, now mock him.

For example; imagine that a famous veteran football coach whose team has been defeated recently, is being criticized and mocked by some young or newly-appointed officials who barely have any knowledge of the game; they even demand he be fired. Then this coach's fans would say:

"Heh! Look who is talking! Jackals deride an old lion!"(= How dare you mock this veteran coach and assume him useless and weak?!)

I have noticed that there is a perfect analog in German:

"Alten Wolf verspotten die Hunde"

which means "Dogs deride an old wolf".

Does English have a direct analog too? If not, is there any idiom, proverb or saying in English which conveys the same meaning?