Bars in the US routinely ID people who are obviously over the age of 21. And then they get weird about foreign passports because...well, because America, I guess. I've sometimes been refused entry despite being clearly over 21 and having my passport with me (or, absurdly, been asked to show another ID, as if a passport wasn't sufficient for buying a beer). Attitudes to IDing people for alcohol are much more pragmatic in the UK.