Yes. Once when I was about 12 to buy cigarettes for someone else in a corner shop in London on a school trip… I always looked older when I was that age.
Once more one day before my 16th birthday. I had to be 16 to get in somewhere and was 15 (only short of 16 by about 12 hours at the time!).
Otherwise no. And yes, both times they believed me. This was long before what is known as “Challenge 21” in the UK.