I have lived in the State for 10 months and have always used my British driving license as an ID. Posto claimed this was "not valid" and that only an American driving license or a passport was a valid form of ID. They refused to service me a glass of wine - I am in my mid thirties!
Later on the meal I had a sip of my friends wine and they took it away as if I had been a naughty child.
Firstly, given that no restaurant or bar has declined my driving license as a valid ID, I question the validity of this approach.
Secondly, they were singularly charmless and rude.
My food and that of my friend was not cooked properly. My fish was under done. However the bread was nice.