If you're under 21 and want to drink on an airplane traveling outside the U.S., you're out of luck if you're flying on United, Delta, American or any other U.S.-based airline. But yes, you can find lower drinking ages on some airlines based elsewhere (emphasis on some; certain airlines don't serve alcohol at all).
The requirement to present identification applies to residents of the Netherlands that are over 13 years old. Police and other officials (such as traffic wardens or customs officials) may ask for it and if you fail to present the right documents you risk having to pay a fine.
In theory the answer is yes, but that does not mean no laws apply. 'The law of the nation where the airline is registered applies on board the aircraft. Although most aviation rules are very similar internationally. '