Originally Posted by
Short hair Francis
Didn't need a fake as a Canadian, we welcome all 19-20 y.o across the border to get drunk

Not sure using a fake is the best idea on a plane considering they know who you are

I've gotten carded at the AC (once, probably because I started with cranberry juice and no alcohol because I wasn't in a big drinking mood).
Quebec (or at least Montreal) welcomes the 18 year olds as well, a rite of passage for many an overentitled New Englander to take a quick jaunt up to YUL and have a few (myself not included), more so before the passport required days. US Customs generally accepts the "I went to Quebec to go drink" explanation without much issue

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OP, do note that the ORD Flagship Lounge is at the far end of one of the concourses. Depending on the gate assignment, it may be a long walk from the FL to your gate, and the ORD FL also doesn't have showers if you're looking for those.