Hi Bence2003, Yes, I should have responded by now.
I am in the USA.
I think 18 and 25 would be heavily boxer-briefs, even some trunks. Almost nothing else except for athletic events. Maybe some boxers at 25ish, but much heavier boxer-briefs.
30's might be an even split between boxers and boxer-briefs.
40's is probably a little bit of everything, with briefs making an appearance.
50's is when you see men of a previous generation show up where briefs was the cool underwear.
But once you get to late 70s/80s, it's boxers again. It's almost like boys rebel against what their father's generation thought was cool.