Originally Posted by Shareholder

It would seem that if AC issued you a MLL card, knowing both your age and the age of majority at most of their lounges, the issue may be mute as far as they're concerned. It appears you've never been "carded" [i.e. birth certificate/driver's license] before, so I should not think this will become an issue unless you look very young, or the name on the MLL card does not match the name on your boarding pass.