What are you rambling about? Op said 18. Drinking is legal everywhere in Europe if you are 18. You know why? Because you are an adult. So you can also fuck everyone while drinking, even 90 year old dudes/dudettes, you know why? Because you are an adult.
You said that being able to legally have sex with someone but that someone not being old enough to legally drink in public is purely a US thing. Taking Germany’s law as an example, I explained how that was not purely a US thing: It’s also the case in Germany, just with the ages shifted downwards quite a bit.