The first time I went to buy booze on my eighteenth birthday, they didn't ID me! I was so dreadfully disappointed.
Then, to really rub it in, I walk to the tobacco kiosk got ID'd for it. The cheek! At this time, the age for buying it was 16 still (I'm in the UK, the was a few years ago).
I look fairly young for my age (20), and so get ID'd all the time. Vendors are usually quite surprised I'm that old.
Well, we can't all have the gift of eternal youth, but you're damn right I'm gonna milk it for what it's worth.