What is the secret to looking youthful? 🙂 I am in my early 30’s and cant remember the last time I was ID’d for proof of age. You should look at it as a compliment; however I do agree that common sense should have prevailed in your case.
I too have been was asked in a Duty Free store of proof that my boarding card matched my ID. I do know for a fact that people who do have airside passes do go through very strong security checks before being employed and doubt the passport would have been taken out of your site. It sounds like that the shop needs to review its customer service policy/process so it doesn’t cause offence.