I'm 27, and am 5'2" with a little face and big eyes. For YEARS, I got asked for ID when buying cigs/alcohol. It drove me mental at the time - I really detested it. Here the smoking age is 16 so I was regularly asked until I was about 23. Some nasty old bat asked me if I was 16, a couple of years ago. I replied "No, dear, I'm 25."
After that it didn't happen much, apart from one little incident in 2004. I had to show my passport to get into a club... at the age of 26.
It hasn't happened for over a year. It pissed me off something chronic when it happened all the time, but now, I don't care anymore. I used to get exceptionally irritated when people told me I'd be glad of it one day, but BonoVoxSuperstar is right, I'm afraid.I still fully empathise with anyone who's been irritated by this.
I worked at a petrol station before I went to uni. I remember being infuriated when some arrogant 16 year old imbecile, who was queueing at my till, turned around to his mate and said "watch me get asked for ID by someone younger than me." I was 21!
That said... I once had to ask a 22 year old to prove his age. He did look about 12, but I was a bit embarrassed when he produced his driving license and various other things. His friend thought it was hilarious. I hated doing it, but if I'd sold cigarettes to some underage brat (who were ALWAYS trying), I could have been fined £1000 and been sacked for gross misconduct. So I do feel for the unfortunate staff that have no choice but to ask.