Can the pilot refuse to board a drunken passenger? Does is true that American may import to their country alcohol only when they 21?

[Superfluous J]

14 minutes ago, DDE said:

It’s been exactly a week, and we’ve got another case against alcohol onboard. FV5863 has had an emergency landing in Sochi. This time, our chivalrous enebriated hero clobbered a stewardess.

Just a guess, but I'm betting they didn't land because of the alcohol.

[kerbiloid]

If they denied the alcohol-challenged passenger's flight, they would have no need to land.

 

[magnemoe]

6 hours ago, DDE said:

It’s been exactly a week, and we’ve got another case against alcohol onboard. FV5863 has had an emergency landing in Sochi. This time, our chivalrous enebriated hero clobbered a stewardess.

People getting angry then drunk should not under any circumstances drink while flying. Pilot will do an emergency landing and dump you, company will then bill you for the added cost, extra time for crew another landing of plane with fuel used and wear on plane. This is expensive seriously expensive, you could also end up anyplace on earth like Siberia or Guam and have to buy another ticket home.
Airline can refuse you to board if too drunk but this require you to be very drunk, way more than an respectable bar would refuse to serve you. 
Drunk and angry is obviously way more dangerous than flirting badly with fight attendants. 

Note don't sing load and badly in business class during the night. This will get you kicked down to economy very fast. the others paid one grand to sleep on the plane. 

No age regulations for buying alcohol or gambling are not enforced outside the country. Laws against drunkenness can be way higher on the other hand. 
In Norway driving an car while drunk will send you to jail. 

[kerbiloid]

Long ago the things were so much easier.
A bottle of rum, a charged pistol, an uninhabited island...