What Does Donkey’s Years Mean? Why Brits Say The Odd Phrase
A 1916 novel by E. V. Lucas, The Vermillion Box, has the following sentence: “Now for my first bath for what the men call ‘Donkey’s ears,’ meaning years and years.”
Article source: https://www.huffingtonpost.co.uk/entry/donkeys-years-meaning-explained-dictionary_uk_6a294f24e4b0a99062fa9a04