An 87-year-old man was asked to prove he was over 21 when he tried to buy a bottle of sherry in a York supermarket.
The former Lord Mayor of York, Jack Archer, said he was shocked - but flattered - when asked the question by staff at Morrisons in Acomb.
He said: "I don't look my age but I certainly don't look young enough to be in trouble for underage drinking."
Morrisons said staff had to ask anyone buying alcohol to confirm they were over 21, or provide proof of age.
Mr Archer said he often had a small glass of sherry at bedtime to help him sleep.
He said: "I was taken aback really. Afterwards I thought I should have showed them my bus pass and that would have proved how old I was.
"I must admit the lady wasn't too persistent and I realised she was only doing what she's been told to do."
A Morrisons spokesman said: "This is done with the best of intentions and we would hope it is taken in good humour by those obviously over the age of 21, as we do not wish to cause offence and no disrespect is intended.
"We take our responsibility with regard to selling alcohol very seriously and all our stores operate the Task 21 scheme, which addresses the difficulties staff face in being able to determine if a customer is legally old enough to buy alcohol.
"To further limit any element of doubt, staff at the Acomb store are required to ask anyone buying alcohol to confirm that they are over 21."
Anyone who appears to be under 21 has to provide proof they are old enough to buy alcohol.