In Japan, people who are under 20 years old are prohibited tofrom buying and drinking alcohol, so I can't drink yet. In Japan, people who are under 20 years old are prohibited from buying and drinking alcohol, so I can't drink yet.

Prohibit: - https://forum.wordreference.com/threads/prohibit-to-from.1471322/ - https://www.btb.termiumplus.gc.ca/tpv2guides/guides/wrtps/index-eng.html?lang=eng&lettr=indx_catlog_p&page=9eF1vQ8H3lmk.html

Some of my friends are over 20, and they often drink liquor. Some of my friends are over 20, and they often drink liquor.

It makes more sense to write out the number as "twenty" to me, but this is probably fine.

I can't understand why they prefer to drink because I think drinking has many demeritownsides and only a few meritupsides. I can't understand why they prefer to drink because I think drinking has many downsides and only a few upsides.

The sentence makes sense, but demerits is rather formal and not commonly used.

I can't understand why they preferlike to drink because I think drinking has many demeritnegatives and only a few meritpositives. I can't understand why they like to drink because I think drinking has many negatives and only a few positives.

"Prefer" requires the existence of an alternative (explicitly or implicitly).

The biggest demeritnegative is damage to health. The biggest negative is damage to health.

Of course, moderate drinking is not a problem, but there are many incidentproblems that are caused by alcohol. Of course, moderate drinking is not a problem, but there are many problems that are caused by alcohol.

Incidents usually refer to an event (eg. car crash). 'Problems' is more suitable here since you're talking about 'health problems' as well.

Of course, moderate drinking is not a problem, but there are many incidentproblems that are caused by alcohol. Of course, moderate drinking is not a problem, but there are many problems that are caused by alcohol.

"Incident" refers to specific events

For example, alcohol harms the liver, orand many people are suffering from alcohol addiction. For example, alcohol harms the liver, and many people are suffering from alcohol addiction.

"And" sounds better to me here because both things are general statements that are true. "Or" would have fine if you had combined the sentences into something like "problems… such as harm caused to the liver or alcohol addiction." You could also have written: "For example, people suffer from liver damage from alcohol, or they are addicted to it."

Drunken driving often kills people. Drunk driving often kills people.

In addition, I don't think alcohol is delicioustastes good. In addition, I don't think alcohol tastes good.

The original was grammatical, but "delicious" sounds like you are trying to saying that alcohol neither tastes bad nor particularly good: "I don't think alcohol is delicious [but it does taste fine to me]." https://en.wikipedia.org/wiki/Litotes

I have secretly tried to beer, wine, and whiskey, but all of them were not good for meI did not like any of them. I have secretly tried beer, wine, and whiskey, but I did not like any of them.

I secretly tried to beer, wine, and whiskey, but allnone of them were nottasted good forto me. I secretly tried beer, wine, and whiskey, but none of them tasted good to me.

"Good for me": has a positive effect

Besides, a hangover maybeight ruins a good feeling. Besides, a hangover might ruin a good feeling.

Besides, a hangover maybe ruins a good feeling. Besides, a hangover may ruin a good feeling.