Think it was just your peer group then. It's still very much a thing. Did it in my youth twice, once at 16 years once at 18 around 2010. I know my cousin who is >10 years younger than me also did it sometime in the last 5 years. Among my peers it was fairly common but it was not done by the majority. If I'd have to guess I'd say 10-20% did it at some point towards the end of highschool.
We also did party trips but that's just a different kind of trip and doesn't really mean the other thing is dead.
Yes, very much still a thing. We saw Interrail travellers of all ages. Lots of students going on a big adventure - but a decent number of more experienced travellers seeing the sights.
https://www.interrail.com/en/magazine/did-you-know/rail-reca...