How is the drinking culture of Europe and America different? In the sense of the difference between us (in Europe) 18 and the USA 21 years?

There is a huge difference.  In Europe, they drink lukewarm beer that tastes somewhat like urine.  In America, they drink ice cold urine that tastes somewhat like beer.

I have lived in both continents and have made my own observations about cultural differences, so here is my general view:

Europeans are more social people who live close together, and alcohol is allowed by society from an early age, so people get together to drink and talk. Teenagers drink a lot in pubs, bars and clubs. It is about having a good time. 

Americans are less social, and alcohol is strictly forbidden in the US before the age of 21. Teenagers buy packs of beer and drink until they are drunk. The aim is not to enjoy the taste, but to be as drunk as possible. Also, because alcohols is less readily available for teenagers, a lot of them turn to marijuana/cannabis and other drugs. 

The US has the world's highest rate of illegal drug use. 

in some european countries its legal to drink certain alcoholic beverages much earlier with adult supervision.

the reason is simple.   americans have worse judgement than europeans. for example: europeans realized long ago people dont need an armory in their home.

also, only in america EVERYTHING is political, including scietific facts (global warming).   only in america, the people WANT to pay thousands of dollars for meds and college because they dont want to be "commies".

Drinking Culture:  

Asian dude goes to the bar with 4 friends ..... and .... went to the counter to buy beer ...... he bought a case of 24 for all the friends + 5 shots + foodWhite dud goes to the bar with 4 friends ........ each paid for their own drinks and food

Very few in the US get arrested for underage drinking unless they were also driving, or destroyed property.  The vast majority of the time the cops dumped it out and let one go, unless intoxicated, then parents would be brought in.

I do not understand why the US needs to be higher then the world. It used to be lower, 18 for most places when I grew up. But in the US, the lower the drinking age, the more deaths from drinking and driving. In my lifetime it has bounced, 18 to 21 then down again, then up again. Becouse when they did lower it, same result, idiots drank, drove, and created deaths and destruction.

i think you should drink whatever you want

No one in America really cares where their liquor is produced. As long as they enjoy the product and consider it to be of high quality, it's all good.